cloning and stem cell technology essay

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Cloning produces human embryonic stem cells.

Fine-tuning of technique used in other animals could enable personalized medicine

CLONING FEAT Using a laser and a tiny needle, researchers suck DNA from a human egg, the first step of a newly revised process that created human embryonic stem cells for the first time. 

Courtesy of M. Tachibana

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By Meghan Rosen

May 15, 2013 at 4:14 pm

View the video For the first time, scientists have created human embryonic stem cells by transferring the nucleus of a mature cell into an egg. The cloning technique could nudge the dream of personalized medicine closer to reality, researchers suggest May 15 in Cell .

“It’s a huge, landmark achievement,” says stem cell biologist George Daley at Children’s Hospital Boston and Harvard University. Creating embryonic stem cells by nuclear transfer in humans, he says, is “the next major technological advance since Dolly.”

The famous sheep Dolly was the first mammal cloned by the nuclear transfer technique, injecting the nucleus of a cell from one adult sheep into the egg of another. Since the animal’s birth in 1996, scientists around the world have tried to duplicate the technique in human cells.

Unlike adult cells, which have already followed a path to become, say, heart cells, neurons or skin cells, embryonic stem cells are uniquely poised to become any cell in the body. And if scientists could make these stem cells from a patient’s own tissues, once-untreatable conditions could perhaps be cured by replacing damaged cells with healthy ones.

But creating embryonic stem cells in humans has proven tricky, says Kathrin Plath, a stem cell biologist at the University of California, Los Angeles. No one knew why the technique worked in other mammals but not humans. Researchers had to figure out the best way to ease out an egg’s DNA, slip in a new nucleus and then cue the egg to divide and grow. In 2011, scientists came close, but the egg stalled out after three divisions, producing just eight cells.

In 2007, a new way to make stem cells dazzled scientists in the field ( SN: 11/24/07, p. 323 ). By dosing human cells with a small cocktail of molecules, researchers pushed a reset button that turned adult cells back into embryonic-like ones called induced pluripotent stem cells, or iPS cells.

“For the last six or seven years, virtually all of us have ended our nuclear transfer efforts and switched over to iPS cells,” Daley says.

But a team led by Shoukhrat Mitalipov of the Oregon National Primate Research Center in Beaverton kept plugging away at nuclear transfer, first using rhesus macaques, and then with human cells.

One key change was adding caffeine to the eggs before DNA transfer, says stem cell biologist James Byrne of UCLA, who was not involved in the new work. Caffeine acts like a set of chemical reins, holding back the egg’s development until researchers inject a new nucleus. The new protocol also features other tweaks such as examining the eggs under polarized instead of ultraviolet light, which can damage the egg.

Using the new method, researchers made embryonic stem cells from an egg and the nucleus of a young boy’s skin cell. The new cells can grow and divide to form a mass of embryonic stem cells just like those derived from fertilized embryos, Mitalipov said in a press briefing May 14.

And when researchers ground the cells up and compared the genetic bits to those in embryonic stem cells, they didn’t see much of a difference. Virtually all of the new cells’ genes were reset to their embryonic states.

What’s more, Byrne says, the approach boasts “dramatically improved efficiency.” Instead of burning through thousands of eggs to make a single embryonic stem cell line, Mitalipov’s group could use just two eggs.

The new cells may have advantages over iPS cells in treating some genetic flaws that lurk in mitochondria, little cellular power plants that carry their own DNA. By putting the nucleus of a patient’s skin cell into a fresh egg with healthy mitochondria, scientists could potentially make a customized therapy that erases the defects, Mitalipov said.

The work “is certainly impressive,” says developmental biologist John Gurdon, who shared the 2012 Nobel Prize in physiology or medicine for pioneering the nuclear transfer technique to clone a frog.

Next, Gurdon says, researchers ought to compare the new embryonic stem cells with iPS cells. A side-by-side look might provide clues to how resetting adult cells actually works. If they can figure out why Mitalipov’s nuclear transfer method is so successful, researchers might be able to improve the technique to make iPS cells and avoid having to retrieve eggs from volunteers.

Embryonic stem cells made using this method have the potential to treat spinal cord injuries and diseases such as diabetes or Parkinson’s, says Dietrich Egli, a stem cell biologist at the New York Stem Cell Foundation. “I’m very confident that such cells will be used for therapies in humans in the future.”

Researchers used a modified technique to create human embryonic stem cells using adult cell nuclei and egg cells. The scientists were then able to turn the immature cells into a variety of tissue types, like these contracting heart cells. Courtesy of Cell, Tachibana et al.

Back Story | HISTORY OF CLONING RESEARCH

Advancement in animal cloning has occurred against a backdrop of ethical debates and scientific fraud.

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• Introduction to Ecology; Major patterns in Earth’s climate
• Behavioral Ecology
• Population Ecology 1
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• Strong Inference
• What is life?
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• Evolution by Natural Selection
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• Population Genetics: the Hardy-Weinberg Principle
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• Oxidative pathways: electrons from food to electron carriers
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• Why are plants green, and how did chlorophyll take over the world? (Converting light energy into chemical energy)
• Carbon fixation
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Cloning and Stem Cells

• Adaptive Immunity
• Human evolution and adaptation

Learning Objectives

• Describe the basic procedure for cloning vertebrate animals via somatic cell nuclear transfer to enucleated eggs
• Discuss the difficulties and obstacles, both technical and ethical, for the use of animal cloning
• Compare and contrast therapeutic cloning versus reproductive cloning
• Describe the procedure for obtaining embryonic stem cells
• Compare and contrast embryonic stem cells with alternative stem cell sources (iPSCs and adult stem cells)

Gene therapy works best by genetically repairing a patient’s stem cells. The easiest source of stem cells are from early embryos. The intersection of stem cell technology, genetic engineering, and cloning poses both scientific and ethical challenges. Before we consider how molecular cloning works, watch this video to learn what stem cells are and how they form:

From the video, we now know that stems cells have two key features: differentiation and self-renewal. This can help us understand some strange things about some cell types. Differentiation, the process of a cell type becoming specialized, explains how our different tissues and structures form from a single zygote cell as multicellular organisms develop and grow. Self-renewal means that a cell can replicate itself faithfully. Red blood cells, which do not have nuclei at all, don’t contain the genomic DNA that all other body cells have, and without the genetic code these cells cannot self-renew. Instead, new red blood cells are generated from hematopoietic stem cells found in bone marrow.

Reproductive Cloning

Many organisms, including all bacteria and archaea and some eukaryotes, reproduce asexually. Asexual reproduction results in progeny that are genetically identical to the parent, meaning that they are “clones” of the parent.

Most complex, multicellular eukaryotes, however, reproduce only sexually. Two haploid gametes unite to form a diploid cell, called a zygote, that reproduces mitotically to form all the somatic cells of a complex multicellular organism. During mitotic cell divisions, various cells express different sets of genes to differentiate into different organs, tissues, and cell types. Two fundamental questions of biology are: 1) how do genes regulate the process of development, and 2) do somatic cells undergo irreversible genetic changes as they differentiate.

Early experiments with cloning in plants showed that individual somatic cells (cells that do not form sperm or egg) could form complete, new clonal plants, indicating that the somatic cells had no irreversible changes in their genome compared to the original fertilized egg cell.

The first studies to test whether vertebrate animals could be cloned used a technique called somatic cell nuclear transfer (SCNT), where nuclei from somatic cells were transferred to an egg cell whose own nucleus had been removed.

Early studies with enucleated frog eggs found that donor nuclei from early embryos supported development of a complete adult animal, but nuclei from tadpoles or adult frogs could not. These early results suggested that as vertebrate animals progressed through embryonic development, birth, and aging, their somatic cell nuclei became “programmed” to differentiate into specialized cells, rather than support embryonic development. We now know that this programming involves reversible modification of chromatin that restricts what genes can be expressed in differentiated cells.

The short video below shows the SCNT process:

In 1996, Ian Wilmut and colleagues found that by arresting adult somatic cell cultures in the cell cycle, he could erase some or most of their nuclear programming. Using cultured mammary gland cells from an adult sheep as the source of donor nuclei, he performed 277 SCNTs to create clone embryos. The embryos that divided normally were implanted into the uterus of foster mother sheep. Only a single lamb, Dolly, was successfully born alive and healthy from the 277 attempts. Since then, many other mammalian species have been cloned, with success rates varying from a few to low tens of percent.

This video described how Dolly was cloned as well as other examples of early mammalian cloning experiments: https://www.dnalc.org/view/16992-Cloning-101.html

Mammalian reproductive cloning is still inefficient, with a low success rate, complications during pregnancy, and possible premature aging of the cloned offspring ( https://learn.genetics.utah.edu/content/tech/cloning/cloningrisks/ ). As far as we know, no reproductive cloning of humans has yet been attempted.

Therapeutic Cloning

In contrast to reproductive cloning to create offspring with identical genetic information, therapeutic cloning has a goal to make stem cell lines compatible with the patient to repair a patient’s cells, preferably their stem cells. The stem cell options include adult, modified embryonic, and induced pluripotent stem cells.

Adult Stem Cells

The human body is quite limited in its ability to regenerate or repair injuries or diseases that affect critical organs such as the brain, heart, and pancreas. Tissue and organ regeneration and gene therapy require a source of cells that can differentiate into the desired types of cells and continue to produce those cells for the lifetime of the patient. Adult humans have distinct reservoirs of stem cells , located in different parts of the body (such as the bone marrow). Stem cells, by definition, can continue to divide and both replace themselves and produce progeny cells that differentiate into new cells in their cell lineage, such as blood and immune system cells, or skin cells, or cells that line the gut and airways, or muscle cells. But these adult stem cells are difficult to obtain from a patient, and they are restricted in the types of cells or tissues they can form. For example, the stem cells in the bone marrow can generate both white and red blood cells, but not skin cells or new brain cells or heart muscle or pancreatic beta islet cells (to cure diabetes).

Embryonic stem cells for therapeutic cloning

Cells in an early human embryo, however, are totipotent . Totipotent means they can serve as the basis to form any part of the developing body. Even after the developing zygote differentiates into three germ layers from which all other tissues arise (day 5 in the image below), the three germ layers retain the ability to specialize in different ways. We call these germ layers pluripotent because each layer can become any body cell type within that layer. These pluripotent cells can be cultured indefinitely as embryonic stem cell lines. Existing human embryonic stem cell lines were derived from the blastocysts of early-stage human embryos created through in vitro fertilization in a fertility clinic. The existing human stem cell lines were generated from surplus embryos from fertility clinics that would have been discarded or put into indefinite cryostorage rather than implanted into a human uterus. Without implantation in a uterus, mammalian embryos cannot develop.

Therapeutic cloning uses enucleated human eggs and somatic cell nuclear transfer technology to create a human embryo that is a genetic clone of the patient. The embryo is destroyed to obtain embryonic stem cells that have the same genotype as the patient. These cells can be cultured indefinitely, and when needed the cells can be hormonally induced to form new tissues and organs that will not be rejected by the patient’s immune system. Human therapeutic cloning – making human embryonic stem cells via somatic cell nuclear transfer – was published for the first time by Tachibana and colleagues in 2013 ( https://doi.org/10.1016/j.cell.2013.05.006 ).

Induced pluripotent stem cells

Beginning in 2006, genetic engineers developed the technology to create a new type of stem cell: induced pluripotent stem cells (iPSCs). iPSCs, created by transforming adult differentiated cells (such as fibroblasts or skin cells) with 4-6 different transcription factors that regulate early embryonic cell growth and differentiation, have many of the properties of embryonic stem cells. The question is whether these transcription factor genes can be safely used to transform the patient’s own cells without causing unacceptably high risks of cancer once these cells are reintroduced into the patient’s body. Because iPSCs do not involve destruction of human embryos, they have been the focus of intense research. Should you be interested in learning more, a review by Wilson and Wu (2015) provides a concise description of the state of the research and the challenges in this field.

Stem cell therapy

Stem cells, depending on whether they were obtained from adults, embryos, or induced with transcription factors, can be induced to differentiate into different cell types to generate replacement organs and repair damaged heart muscle, pancreatic beta cells, spinal cord or brain cells. Coupled with genome editing, stem cells could be used to treat patients with genetic disorders.

Cloning and bioethics

The technical obstacles to reproductive and therapeutic cloning will be addressed and overcome as scientific technologies advance. For instance, the advent of CRISPR, discussed in the previous reading, has quickly revolutionized options to create recombinant organisms. However, in 2016 many of the researchers who discovered CRISPR technology called for a moratorium on use of CRISPR for editing human germ cells and embryos. Consideration of ethical barriers is fundamental to regulate how we use technologies and discoveries. Ideas of autonomy, consent, and individual rights craft the ways that bioethicists and others think about topics like human cloning and “designer babies.” Some ethicists argue that the moral stance and place of humans need also be considered (Sandel 2005) when considering human cloning or the use of embryos in research because humans gain access to the ability to change nature through these technologies. Reflecting as individuals and as societies on the ethics of biology and biological technologies is essential work as cloning techniques advance.

UN Sustainable Development Goal (SDG)

SDG 1: No Poverty – Healthcare plays a role in reducing extreme economic inequalities between and within nations. As new therapies and technologies, such as cloning, become more common, it is necessary to consider the difficulties and obstacles, both technical and ethical, for the use of cloning for healthcare and in increasing food supplies. Who can afford it? By using this technology, what changes take place economically, and for whom? Access to the resources produced by such technologies includes considerations on how to responsibly use biotechnology while minimizing negative impacts on the environment and society across the globe.

Resources and References

Slides for the videos above: Cloning_StemCells

Wilson, KD and JC Wu (2015) Induced Pluripotent Stem Cells, JAMA. 313(16):1613-1614. doi:10.1001/jama.2015.1846

https://learn.genetics.utah.edu/content/tech/cloning/whatiscloning

https://learn.genetics.utah.edu/content/tech/cloning/clickandclone/ go through the steps to clone a mouse using somatic cell nuclear transfer technology

One Response to Cloning and Stem Cells

Human therapeutic cloning – making human embryonic stem cells via somatic cell nuclear transfer – was published for the first time in 2013: http://www.npr.org/sections/health-shots/2013/05/15/183916891/scientists-clone-human-embryos-to-make-stem-cells

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Stem cells: past, present, and future

• Wojciech Zakrzewski 1 ,
• Maciej Dobrzyński 2 ,
• Maria Szymonowicz 1 &
• Zbigniew Rybak 1  

Stem Cell Research & Therapy volume  10 , Article number:  68 ( 2019 ) Cite this article

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In recent years, stem cell therapy has become a very promising and advanced scientific research topic. The development of treatment methods has evoked great expectations. This paper is a review focused on the discovery of different stem cells and the potential therapies based on these cells. The genesis of stem cells is followed by laboratory steps of controlled stem cell culturing and derivation. Quality control and teratoma formation assays are important procedures in assessing the properties of the stem cells tested. Derivation methods and the utilization of culturing media are crucial to set proper environmental conditions for controlled differentiation. Among many types of stem tissue applications, the use of graphene scaffolds and the potential of extracellular vesicle-based therapies require attention due to their versatility. The review is summarized by challenges that stem cell therapy must overcome to be accepted worldwide. A wide variety of possibilities makes this cutting edge therapy a turning point in modern medicine, providing hope for untreatable diseases.

Stem cell classification

Stem cells are unspecialized cells of the human body. They are able to differentiate into any cell of an organism and have the ability of self-renewal. Stem cells exist both in embryos and adult cells. There are several steps of specialization. Developmental potency is reduced with each step, which means that a unipotent stem cell is not able to differentiate into as many types of cells as a pluripotent one. This chapter will focus on stem cell classification to make it easier for the reader to comprehend the following chapters.

Totipotent stem cells are able to divide and differentiate into cells of the whole organism. Totipotency has the highest differentiation potential and allows cells to form both embryo and extra-embryonic structures. One example of a totipotent cell is a zygote, which is formed after a sperm fertilizes an egg. These cells can later develop either into any of the three germ layers or form a placenta. After approximately 4 days, the blastocyst’s inner cell mass becomes pluripotent. This structure is the source of pluripotent cells.

Pluripotent stem cells (PSCs) form cells of all germ layers but not extraembryonic structures, such as the placenta. Embryonic stem cells (ESCs) are an example. ESCs are derived from the inner cell mass of preimplantation embryos. Another example is induced pluripotent stem cells (iPSCs) derived from the epiblast layer of implanted embryos. Their pluripotency is a continuum, starting from completely pluripotent cells such as ESCs and iPSCs and ending on representatives with less potency—multi-, oligo- or unipotent cells. One of the methods to assess their activity and spectrum is the teratoma formation assay. iPSCs are artificially generated from somatic cells, and they function similarly to PSCs. Their culturing and utilization are very promising for present and future regenerative medicine.

Multipotent stem cells have a narrower spectrum of differentiation than PSCs, but they can specialize in discrete cells of specific cell lineages. One example is a haematopoietic stem cell, which can develop into several types of blood cells. After differentiation, a haematopoietic stem cell becomes an oligopotent cell. Its differentiation abilities are then restricted to cells of its lineage. However, some multipotent cells are capable of conversion into unrelated cell types, which suggests naming them pluripotent cells.

Oligopotent stem cells can differentiate into several cell types. A myeloid stem cell is an example that can divide into white blood cells but not red blood cells.

Unipotent stem cells are characterized by the narrowest differentiation capabilities and a special property of dividing repeatedly. Their latter feature makes them a promising candidate for therapeutic use in regenerative medicine. These cells are only able to form one cell type, e.g. dermatocytes.

Stem cell biology

A blastocyst is formed after the fusion of sperm and ovum fertilization. Its inner wall is lined with short-lived stem cells, namely, embryonic stem cells. Blastocysts are composed of two distinct cell types: the inner cell mass (ICM), which develops into epiblasts and induces the development of a foetus, and the trophectoderm (TE). Blastocysts are responsible for the regulation of the ICM microenvironment. The TE continues to develop and forms the extraembryonic support structures needed for the successful origin of the embryo, such as the placenta. As the TE begins to form a specialized support structure, the ICM cells remain undifferentiated, fully pluripotent and proliferative [ 1 ]. The pluripotency of stem cells allows them to form any cell of the organism. Human embryonic stem cells (hESCs) are derived from the ICM. During the process of embryogenesis, cells form aggregations called germ layers: endoderm, mesoderm and ectoderm (Fig.  1 ), each eventually giving rise to differentiated cells and tissues of the foetus and, later on, the adult organism [ 2 ]. After hESCs differentiate into one of the germ layers, they become multipotent stem cells, whose potency is limited to only the cells of the germ layer. This process is short in human development. After that, pluripotent stem cells occur all over the organism as undifferentiated cells, and their key abilities are proliferation by the formation of the next generation of stem cells and differentiation into specialized cells under certain physiological conditions.

Oocyte development and formation of stem cells: the blastocoel, which is formed from oocytes, consists of embryonic stem cells that later differentiate into mesodermal, ectodermal, or endodermal cells. Blastocoel develops into the gastrula

Signals that influence the stem cell specialization process can be divided into external, such as physical contact between cells or chemical secretion by surrounding tissue, and internal, which are signals controlled by genes in DNA.

Stem cells also act as internal repair systems of the body. The replenishment and formation of new cells are unlimited as long as an organism is alive. Stem cell activity depends on the organ in which they are in; for example, in bone marrow, their division is constant, although in organs such as the pancreas, division only occurs under special physiological conditions.

Stem cell functional division

Whole-body development.

During division, the presence of different stem cells depends on organism development. Somatic stem cell ESCs can be distinguished. Although the derivation of ESCs without separation from the TE is possible, such a combination has growth limits. Because proliferating actions are limited, co-culture of these is usually avoided.

ESCs are derived from the inner cell mass of the blastocyst, which is a stage of pre-implantation embryo ca. 4 days after fertilization. After that, these cells are placed in a culture dish filled with culture medium. Passage is an inefficient but popular process of sub-culturing cells to other dishes. These cells can be described as pluripotent because they are able to eventually differentiate into every cell type in the organism. Since the beginning of their studies, there have been ethical restrictions connected to the medical use of ESCs in therapies. Most embryonic stem cells are developed from eggs that have been fertilized in an in vitro clinic, not from eggs fertilized in vivo.

Somatic or adult stem cells are undifferentiated and found among differentiated cells in the whole body after development. The function of these cells is to enable the healing, growth, and replacement of cells that are lost each day. These cells have a restricted range of differentiation options. Among many types, there are the following:

Mesenchymal stem cells are present in many tissues. In bone marrow, these cells differentiate mainly into the bone, cartilage, and fat cells. As stem cells, they are an exception because they act pluripotently and can specialize in the cells of any germ layer.

Neural cells give rise to nerve cells and their supporting cells—oligodendrocytes and astrocytes.

Haematopoietic stem cells form all kinds of blood cells: red, white, and platelets.

Skin stem cells form, for example, keratinocytes, which form a protective layer of skin.

The proliferation time of somatic stem cells is longer than that of ESCs. It is possible to reprogram adult stem cells back to their pluripotent state. This can be performed by transferring the adult nucleus into the cytoplasm of an oocyte or by fusion with the pluripotent cell. The same technique was used during cloning of the famous Dolly sheep.

hESCs are involved in whole-body development. They can differentiate into pluripotent, totipotent, multipotent, and unipotent cells (Fig.  2 ) [ 2 ].

Changes in the potency of stem cells in human body development. Potency ranges from pluripotent cells of the blastocyst to unipotent cells of a specific tissue in a human body such as the skin, CNS, or bone marrow. Reversed pluripotency can be achieved by the formation of induced pluripotent stem cells using either octamer-binding transcription factor (Oct4), sex-determining region Y (Sox2), Kruppel-like factor 4 (Klf4), or the Myc gene

Pluripotent cells can be named totipotent if they can additionally form extraembryonic tissues of the embryo. Multipotent cells are restricted in differentiating to each cell type of given tissue. When tissue contains only one lineage of cells, stem cells that form them are called either called oligo- or unipotent.

iPSC quality control and recognition by morphological differences

The comparability of stem cell lines from different individuals is needed for iPSC lines to be used in therapeutics [ 3 ]. Among critical quality procedures, the following can be distinguished:

Short tandem repeat analysis—This is the comparison of specific loci on the DNA of the samples. It is used in measuring an exact number of repeating units. One unit consists of 2 to 13 nucleotides repeating many times on the DNA strand. A polymerase chain reaction is used to check the lengths of short tandem repeats. The genotyping procedure of source tissue, cells, and iPSC seed and master cell banks is recommended.

Identity analysis—The unintentional switching of lines, resulting in other stem cell line contamination, requires rigorous assay for cell line identification.

Residual vector testing—An appearance of reprogramming vectors integrated into the host genome is hazardous, and testing their presence is a mandatory procedure. It is a commonly used procedure for generating high-quality iPSC lines. An acceptable threshold in high-quality research-grade iPSC line collections is ≤ 1 plasmid copies per 100 cells. During the procedure, 2 different regions, common to all plasmids, should be used as specific targets, such as EBNA and CAG sequences [ 3 ]. To accurately represent the test reactions, a standard curve needs to be prepared in a carrier of gDNA from a well-characterized hPSC line. For calculations of plasmid copies per cell, it is crucial to incorporate internal reference gDNA sequences to allow the quantification of, for example, ribonuclease P (RNaseP) or human telomerase reverse transcriptase (hTERT).

Karyotype—A long-term culture of hESCs can accumulate culture-driven mutations [ 4 ]. Because of that, it is crucial to pay additional attention to genomic integrity. Karyotype tests can be performed by resuscitating representative aliquots and culturing them for 48–72 h before harvesting cells for karyotypic analysis. If abnormalities are found within the first 20 karyotypes, the analysis must be repeated on a fresh sample. When this situation is repeated, the line is evaluated as abnormal. Repeated abnormalities must be recorded. Although karyology is a crucial procedure in stem cell quality control, the single nucleotide polymorphism (SNP) array, discussed later, has approximately 50 times higher resolution.

Viral testing—When assessing the quality of stem cells, all tests for harmful human adventitious agents must be performed (e.g. hepatitis C or human immunodeficiency virus). This procedure must be performed in the case of non-xeno-free culture agents.

Bacteriology—Bacterial or fungal sterility tests can be divided into culture- or broth-based tests. All the procedures must be recommended by pharmacopoeia for the jurisdiction in which the work is performed.

Single nucleotide polymorphism arrays—This procedure is a type of DNA microarray that detects population polymorphisms by enabling the detection of subchromosomal changes and the copy-neutral loss of heterozygosity, as well as an indication of cellular transformation. The SNP assay consists of three components. The first is labelling fragmented nucleic acid sequences with fluorescent dyes. The second is an array that contains immobilized allele-specific oligonucleotide (ASO) probes. The last component detects, records, and eventually interprets the signal.

Flow cytometry—This is a technique that utilizes light to count and profile cells in a heterogeneous fluid mixture. It allows researchers to accurately and rapidly collect data from heterogeneous fluid mixtures with live cells. Cells are passed through a narrow channel one by one. During light illumination, sensors detect light emitted or refracted from the cells. The last step is data analysis, compilation and integration into a comprehensive picture of the sample.

Phenotypic pluripotency assays—Recognizing undifferentiated cells is crucial in successful stem cell therapy. Among other characteristics, stem cells appear to have a distinct morphology with a high nucleus to cytoplasm ratio and a prominent nucleolus. Cells appear to be flat with defined borders, in contrast to differentiating colonies, which appear as loosely located cells with rough borders [ 5 ]. It is important that images of ideal and poor quality colonies for each cell line are kept in laboratories, so whenever there is doubt about the quality of culture, it can always be checked according to the representative image. Embryoid body formation or directed differentiation of monolayer cultures to produce cell types representative of all three embryonic germ layers must be performed. It is important to note that colonies cultured under different conditions may have different morphologies [ 6 ].

Histone modification and DNA methylation—Quality control can be achieved by using epigenetic analysis tools such as histone modification or DNA methylation. When stem cells differentiate, the methylation process silences pluripotency genes, which reduces differentiation potential, although other genes may undergo demethylation to become expressed [ 7 ]. It is important to emphasize that stem cell identity, together with its morphological characteristics, is also related to its epigenetic profile [ 8 , 9 ]. According to Brindley [ 10 ], there is a relationship between epigenetic changes, pluripotency, and cell expansion conditions, which emphasizes that unmethylated regions appear to be serum-dependent.

hESC derivation and media

hESCs can be derived using a variety of methods, from classic culturing to laser-assisted methodologies or microsurgery [ 11 ]. hESC differentiation must be specified to avoid teratoma formation (see Fig.  3 ).

Spontaneous differentiation of hESCs causes the formation of a heterogeneous cell population. There is a different result, however, when commitment signals (in forms of soluble factors and culture conditions) are applied and enable the selection of progenitor cells

hESCs spontaneously differentiate into embryonic bodies (EBs) [ 12 ]. EBs can be studied instead of embryos or animals to predict their effects on early human development. There are many different methods for acquiring EBs, such as bioreactor culture [ 13 ], hanging drop culture [ 12 ], or microwell technology [ 14 , 15 ]. These methods allow specific precursors to form in vitro [ 16 ].

The essential part of these culturing procedures is a separation of inner cell mass to culture future hESCs (Fig.  4 ) [ 17 ]. Rosowski et al. [ 18 ] emphasizes that particular attention must be taken in controlling spontaneous differentiation. When the colony reaches the appropriate size, cells must be separated. The occurrence of pluripotent cells lasts for 1–2 days. Because the classical utilization of hESCs caused ethical concerns about gastrulas used during procedures, Chung et al. [ 19 ] found out that it is also possible to obtain hESCs from four cell embryos, leaving a higher probability of embryo survival. Additionally, Zhang et al. [ 20 ] used only in vitro fertilization growth-arrested cells.

Culturing of pluripotent stem cells in vitro. Three days after fertilization, totipotent cells are formed. Blastocysts with ICM are formed on the sixth day after fertilization. Pluripotent stem cells from ICM can then be successfully transmitted on a dish

Cell passaging is used to form smaller clusters of cells on a new culture surface [ 21 ]. There are four important passaging procedures.

Enzymatic dissociation is a cutting action of enzymes on proteins and adhesion domains that bind the colony. It is a gentler method than the manual passage. It is crucial to not leave hESCs alone after passaging. Solitary cells are more sensitive and can easily undergo cell death; collagenase type IV is an example [ 22 , 23 ].

Manual passage , on the other hand, focuses on using cell scratchers. The selection of certain cells is not necessary. This should be done in the early stages of cell line derivation [ 24 ].

Trypsin utilization allows a healthy, automated hESC passage. Good Manufacturing Practice (GMP)-grade recombinant trypsin is widely available in this procedure [ 24 ]. However, there is a risk of decreasing the pluripotency and viability of stem cells [ 25 ]. Trypsin utilization can be halted with an inhibitor of the protein rho-associated protein kinase (ROCK) [ 26 ].

Ethylenediaminetetraacetic acid ( EDTA ) indirectly suppresses cell-to-cell connections by chelating divalent cations. Their suppression promotes cell dissociation [ 27 ].

Stem cells require a mixture of growth factors and nutrients to differentiate and develop. The medium should be changed each day.

Traditional culture methods used for hESCs are mouse embryonic fibroblasts (MEFs) as a feeder layer and bovine serum [ 28 ] as a medium. Martin et al. [ 29 ] demonstrated that hESCs cultured in the presence of animal products express the non-human sialic acid, N -glycolylneuraminic acid (NeuGc). Feeder layers prevent uncontrolled proliferation with factors such as leukaemia inhibitory factor (LIF) [ 30 ].

First feeder layer-free culture can be supplemented with serum replacement, combined with laminin [ 31 ]. This causes stable karyotypes of stem cells and pluripotency lasting for over a year.

Initial culturing media can be serum (e.g. foetal calf serum FCS), artificial replacement such as synthetic serum substitute (SSS), knockout serum replacement (KOSR), or StemPro [ 32 ]. The simplest culture medium contains only eight essential elements: DMEM/F12 medium, selenium, NaHCO 3, l -ascorbic acid, transferrin, insulin, TGFβ1, and FGF2 [ 33 ]. It is not yet fully known whether culture systems developed for hESCs can be allowed without adaptation in iPSC cultures.

Turning point in stem cell therapy

The turning point in stem cell therapy appeared in 2006, when scientists Shinya Yamanaka, together with Kazutoshi Takahashi, discovered that it is possible to reprogram multipotent adult stem cells to the pluripotent state. This process avoided endangering the foetus’ life in the process. Retrovirus-mediated transduction of mouse fibroblasts with four transcription factors (Oct-3/4, Sox2, KLF4, and c-Myc) [ 34 ] that are mainly expressed in embryonic stem cells could induce the fibroblasts to become pluripotent (Fig.  5 ) [ 35 ]. This new form of stem cells was named iPSCs. One year later, the experiment also succeeded with human cells [ 36 ]. After this success, the method opened a new field in stem cell research with a generation of iPSC lines that can be customized and biocompatible with the patient. Recently, studies have focused on reducing carcinogenesis and improving the conduction system.

Retroviral-mediated transduction induces pluripotency in isolated patient somatic cells. Target cells lose their role as somatic cells and, once again, become pluripotent and can differentiate into any cell type of human body

The turning point was influenced by former discoveries that happened in 1962 and 1987.

The former discovery was about scientist John Gurdon successfully cloning frogs by transferring a nucleus from a frog’s somatic cells into an oocyte. This caused a complete reversion of somatic cell development [ 37 ]. The results of his experiment became an immense discovery since it was previously believed that cell differentiation is a one-way street only, but his experiment suggested the opposite and demonstrated that it is even possible for a somatic cell to again acquire pluripotency [ 38 ].

The latter was a discovery made by Davis R.L. that focused on fibroblast DNA subtraction. Three genes were found that originally appeared in myoblasts. The enforced expression of only one of the genes, named myogenic differentiation 1 (Myod1), caused the conversion of fibroblasts into myoblasts, showing that reprogramming cells is possible, and it can even be used to transform cells from one lineage to another [ 39 ].

Although pluripotency can occur naturally only in embryonic stem cells, it is possible to induce terminally differentiated cells to become pluripotent again. The process of direct reprogramming converts differentiated somatic cells into iPSC lines that can form all cell types of an organism. Reprogramming focuses on the expression of oncogenes such as Myc and Klf4 (Kruppel-like factor 4). This process is enhanced by a downregulation of genes promoting genome stability, such as p53. Additionally, cell reprogramming involves histone alteration. All these processes can cause potential mutagenic risk and later lead to an increased number of mutations. Quinlan et al. [ 40 ] checked fully pluripotent mouse iPSCs using whole genome DNA sequencing and structural variation (SV) detection algorithms. Based on those studies, it was confirmed that although there were single mutations in the non-genetic region, there were non-retrotransposon insertions. This led to the conclusion that current reprogramming methods can produce fully pluripotent iPSCs without severe genomic alterations.

During the course of development from pluripotent hESCs to differentiated somatic cells, crucial changes appear in the epigenetic structure of these cells. There is a restriction or permission of the transcription of genes relevant to each cell type. When somatic cells are being reprogrammed using transcription factors, all the epigenetic architecture has to be reconditioned to achieve iPSCs with pluripotency [ 41 ]. However, cells of each tissue undergo specific somatic genomic methylation. This influences transcription, which can further cause alterations in induced pluripotency [ 42 ].

Source of iPSCs

Because pluripotent cells can propagate indefinitely and differentiate into any kind of cell, they can be an unlimited source, either for replacing lost or diseased tissues. iPSCs bypass the need for embryos in stem cell therapy. Because they are made from the patient’s own cells, they are autologous and no longer generate any risk of immune rejection.

At first, fibroblasts were used as a source of iPSCs. Because a biopsy was needed to achieve these types of cells, the technique underwent further research. Researchers investigated whether more accessible cells could be used in the method. Further, other cells were used in the process: peripheral blood cells, keratinocytes, and renal epithelial cells found in urine. An alternative strategy to stem cell transplantation can be stimulating a patient’s endogenous stem cells to divide or differentiate, occurring naturally when skin wounds are healing. In 2008, pancreatic exocrine cells were shown to be reprogrammed to functional, insulin-producing beta cells [ 43 ].

The best stem cell source appears to be the fibroblasts, which is more tempting in the case of logistics since its stimulation can be fast and better controlled [ 44 ].

• Teratoma formation assay

The self-renewal and differentiation capabilities of iPSCs have gained significant interest and attention in regenerative medicine sciences. To study their abilities, a quality-control assay is needed, of which one of the most important is the teratoma formation assay. Teratomas are benign tumours. Teratomas are capable of rapid growth in vivo and are characteristic because of their ability to develop into tissues of all three germ layers simultaneously. Because of the high pluripotency of teratomas, this formation assay is considered an assessment of iPSC’s abilities [ 45 ].

Teratoma formation rate, for instance, was observed to be elevated in human iPSCs compared to that in hESCs [ 46 ]. This difference may be connected to different differentiation methods and cell origins. Most commonly, the teratoma assay involves an injection of examined iPSCs subcutaneously or under the testis or kidney capsule in mice, which are immune-deficient [ 47 ]. After injection, an immature but recognizable tissue can be observed, such as the kidney tubules, bone, cartilage, or neuroepithelium [ 30 ]. The injection site may have an impact on the efficiency of teratoma formation [ 48 ].

There are three groups of markers used in this assay to differentiate the cells of germ layers. For endodermal tissue, there is insulin/C-peptide and alpha-1 antitrypsin [ 49 ]. For the mesoderm, derivatives can be used, e.g. cartilage matrix protein for the bone and alcian blue for the cartilage. As ectodermal markers, class III B botulin or keratin can be used for keratinocytes.

Teratoma formation assays are considered the gold standard for demonstrating the pluripotency of human iPSCs, demonstrating their possibilities under physiological conditions. Due to their actual tissue formation, they could be used for the characterization of many cell lineages [ 50 ].

Directed differentiation

To be useful in therapy, stem cells must be converted into desired cell types as necessary or else the whole regenerative medicine process will be pointless. Differentiation of ESCs is crucial because undifferentiated ESCs can cause teratoma formation in vivo. Understanding and using signalling pathways for differentiation is an important method in successful regenerative medicine. In directed differentiation, it is likely to mimic signals that are received by cells when they undergo successive stages of development [ 51 ]. The extracellular microenvironment plays a significant role in controlling cell behaviour. By manipulating the culture conditions, it is possible to restrict specific differentiation pathways and generate cultures that are enriched in certain precursors in vitro. However, achieving a similar effect in vivo is challenging. It is crucial to develop culture conditions that will allow the promotion of homogenous and enhanced differentiation of ESCs into functional and desired tissues.

Regarding the self-renewal of embryonic stem cells, Hwang et al. [ 52 ] noted that the ideal culture method for hESC-based cell and tissue therapy would be a defined culture free of either the feeder layer or animal components. This is because cell and tissue therapy requires the maintenance of large quantities of undifferentiated hESCs, which does not make feeder cells suitable for such tasks.

Most directed differentiation protocols are formed to mimic the development of an inner cell mass during gastrulation. During this process, pluripotent stem cells differentiate into ectodermal, mesodermal, or endodermal progenitors. Mall molecules or growth factors induce the conversion of stem cells into appropriate progenitor cells, which will later give rise to the desired cell type. There is a variety of signal intensities and molecular families that may affect the establishment of germ layers in vivo, such as fibroblast growth factors (FGFs) [ 53 ]; the Wnt family [ 54 ] or superfamily of transforming growth factors—β(TGFβ); and bone morphogenic proteins (BMP) [ 55 ]. Each candidate factor must be tested on various concentrations and additionally applied to various durations because the precise concentrations and times during which developing cells in embryos are influenced during differentiation are unknown. For instance, molecular antagonists of endogenous BMP and Wnt signalling can be used for ESC formation of ectoderm [ 56 ]. However, transient Wnt and lower concentrations of the TGFβ family trigger mesodermal differentiation [ 57 ]. Regarding endoderm formation, a higher activin A concentration may be required [ 58 , 59 ].

There are numerous protocols about the methods of forming progenitors of cells of each of germ layers, such as cardiomyocytes [ 60 ], hepatocytes [ 61 ], renal cells [ 62 ], lung cells [ 63 , 64 ], motor neurons [ 65 ], intestinal cells [ 66 ], or chondrocytes [ 67 ].

Directed differentiation of either iPSCs or ESCs into, e.g. hepatocytes, could influence and develop the study of the molecular mechanisms in human liver development. In addition, it could also provide the possibility to form exogenous hepatocytes for drug toxicity testing [ 68 ].

Levels of concentration and duration of action with a specific signalling molecule can cause a variety of factors. Unfortunately, for now, a high cost of recombinant factors is likely to limit their use on a larger scale in medicine. The more promising technique focuses on the use of small molecules. These can be used for either activating or deactivating specific signalling pathways. They enhance reprogramming efficiency by creating cells that are compatible with the desired type of tissue. It is a cheaper and non-immunogenic method.

One of the successful examples of small-molecule cell therapies is antagonists and agonists of the Hedgehog pathway. They show to be very useful in motor neuron regeneration [ 69 ]. Endogenous small molecules with their function in embryonic development can also be used in in vitro methods to induce the differentiation of cells; for example, retinoic acid, which is responsible for patterning the nervous system in vivo [ 70 ], surprisingly induced retinal cell formation when the laboratory procedure involved hESCs [ 71 ].

The efficacy of differentiation factors depends on functional maturity, efficiency, and, finally, introducing produced cells to their in vivo equivalent. Topography, shear stress, and substrate rigidity are factors influencing the phenotype of future cells [ 72 ].

The control of biophysical and biochemical signals, the biophysical environment, and a proper guide of hESC differentiation are important factors in appropriately cultured stem cells.

Stem cell utilization and their manufacturing standards and culture systems

The European Medicines Agency and the Food and Drug Administration have set Good Manufacturing Practice (GMP) guidelines for safe and appropriate stem cell transplantation. In the past, protocols used for stem cell transplantation required animal-derived products [ 73 ].

The risk of introducing animal antigens or pathogens caused a restriction in their use. Due to such limitations, the technique required an obvious update [ 74 ]. Now, it is essential to use xeno-free equivalents when establishing cell lines that are derived from fresh embryos and cultured from human feeder cell lines [ 75 ]. In this method, it is crucial to replace any non-human materials with xeno-free equivalents [ 76 ].

NutriStem with LN-511, TeSR2 with human recombinant laminin (LN-511), and RegES with human foreskin fibroblasts (HFFs) are commonly used xeno-free culture systems [ 33 ]. There are many organizations and international initiatives, such as the National Stem Cell Bank, that provide stem cell lines for treatment or medical research [ 77 ].

Stem cell use in medicine

Stem cells have great potential to become one of the most important aspects of medicine. In addition to the fact that they play a large role in developing restorative medicine, their study reveals much information about the complex events that happen during human development.

The difference between a stem cell and a differentiated cell is reflected in the cells’ DNA. In the former cell, DNA is arranged loosely with working genes. When signals enter the cell and the differentiation process begins, genes that are no longer needed are shut down, but genes required for the specialized function will remain active. This process can be reversed, and it is known that such pluripotency can be achieved by interaction in gene sequences. Takahashi and Yamanaka [ 78 ] and Loh et al. [ 79 ] discovered that octamer-binding transcription factor 3 and 4 (Oct3/4), sex determining region Y (SRY)-box 2 and Nanog genes function as core transcription factors in maintaining pluripotency. Among them, Oct3/4 and Sox2 are essential for the generation of iPSCs.

Many serious medical conditions, such as birth defects or cancer, are caused by improper differentiation or cell division. Currently, several stem cell therapies are possible, among which are treatments for spinal cord injury, heart failure [ 80 ], retinal and macular degeneration [ 81 ], tendon ruptures, and diabetes type 1 [ 82 ]. Stem cell research can further help in better understanding stem cell physiology. This may result in finding new ways of treating currently incurable diseases.

Haematopoietic stem cell transplantation

Haematopoietic stem cells are important because they are by far the most thoroughly characterized tissue-specific stem cell; after all, they have been experimentally studied for more than 50 years. These stem cells appear to provide an accurate paradigm model system to study tissue-specific stem cells, and they have potential in regenerative medicine.

Multipotent haematopoietic stem cell (HSC) transplantation is currently the most popular stem cell therapy. Target cells are usually derived from the bone marrow, peripheral blood, or umbilical cord blood [ 83 ]. The procedure can be autologous (when the patient’s own cells are used), allogenic (when the stem cell comes from a donor), or syngeneic (from an identical twin). HSCs are responsible for the generation of all functional haematopoietic lineages in blood, including erythrocytes, leukocytes, and platelets. HSC transplantation solves problems that are caused by inappropriate functioning of the haematopoietic system, which includes diseases such as leukaemia and anaemia. However, when conventional sources of HSC are taken into consideration, there are some important limitations. First, there is a limited number of transplantable cells, and an efficient way of gathering them has not yet been found. There is also a problem with finding a fitting antigen-matched donor for transplantation, and viral contamination or any immunoreactions also cause a reduction in efficiency in conventional HSC transplantations. Haematopoietic transplantation should be reserved for patients with life-threatening diseases because it has a multifactorial character and can be a dangerous procedure. iPSC use is crucial in this procedure. The use of a patient’s own unspecialized somatic cells as stem cells provides the greatest immunological compatibility and significantly increases the success of the procedure.

Stem cells as a target for pharmacological testing

Stem cells can be used in new drug tests. Each experiment on living tissue can be performed safely on specific differentiated cells from pluripotent cells. If any undesirable effect appears, drug formulas can be changed until they reach a sufficient level of effectiveness. The drug can enter the pharmacological market without harming any live testers. However, to test the drugs properly, the conditions must be equal when comparing the effects of two drugs. To achieve this goal, researchers need to gain full control of the differentiation process to generate pure populations of differentiated cells.

Stem cells as an alternative for arthroplasty

One of the biggest fears of professional sportsmen is getting an injury, which most often signifies the end of their professional career. This applies especially to tendon injuries, which, due to current treatment options focusing either on conservative or surgical treatment, often do not provide acceptable outcomes. Problems with the tendons start with their regeneration capabilities. Instead of functionally regenerating after an injury, tendons merely heal by forming scar tissues that lack the functionality of healthy tissues. Factors that may cause this failed healing response include hypervascularization, deposition of calcific materials, pain, or swelling [ 84 ].

Additionally, in addition to problems with tendons, there is a high probability of acquiring a pathological condition of joints called osteoarthritis (OA) [ 85 ]. OA is common due to the avascular nature of articular cartilage and its low regenerative capabilities [ 86 ]. Although arthroplasty is currently a common procedure in treating OA, it is not ideal for younger patients because they can outlive the implant and will require several surgical procedures in the future. These are situations where stem cell therapy can help by stopping the onset of OA [ 87 ]. However, these procedures are not well developed, and the long-term maintenance of hyaline cartilage requires further research.

Osteonecrosis of the femoral hip (ONFH) is a refractory disease associated with the collapse of the femoral head and risk of hip arthroplasty in younger populations [ 88 ]. Although total hip arthroplasty (THA) is clinically successful, it is not ideal for young patients, mostly due to the limited lifetime of the prosthesis. An increasing number of clinical studies have evaluated the therapeutic effect of stem cells on ONFH. Most of the authors demonstrated positive outcomes, with reduced pain, improved function, or avoidance of THA [ 89 , 90 , 91 ].

Rejuvenation by cell programming

Ageing is a reversible epigenetic process. The first cell rejuvenation study was published in 2011 [ 92 ]. Cells from aged individuals have different transcriptional signatures, high levels of oxidative stress, dysfunctional mitochondria, and shorter telomeres than in young cells [ 93 ]. There is a hypothesis that when human or mouse adult somatic cells are reprogrammed to iPSCs, their epigenetic age is virtually reset to zero [ 94 ]. This was based on an epigenetic model, which explains that at the time of fertilization, all marks of parenteral ageing are erased from the zygote’s genome and its ageing clock is reset to zero [ 95 ].

In their study, Ocampo et al. [ 96 ] used Oct4, Sox2, Klf4, and C-myc genes (OSKM genes) and affected pancreas and skeletal muscle cells, which have poor regenerative capacity. Their procedure revealed that these genes can also be used for effective regenerative treatment [ 97 ]. The main challenge of their method was the need to employ an approach that does not use transgenic animals and does not require an indefinitely long application. The first clinical approach would be preventive, focused on stopping or slowing the ageing rate. Later, progressive rejuvenation of old individuals can be attempted. In the future, this method may raise some ethical issues, such as overpopulation, leading to lower availability of food and energy.

For now, it is important to learn how to implement cell reprogramming technology in non-transgenic elder animals and humans to erase marks of ageing without removing the epigenetic marks of cell identity.

Cell-based therapies

Stem cells can be induced to become a specific cell type that is required to repair damaged or destroyed tissues (Fig.  6 ). Currently, when the need for transplantable tissues and organs outweighs the possible supply, stem cells appear to be a perfect solution for the problem. The most common conditions that benefit from such therapy are macular degenerations [ 98 ], strokes [ 99 ], osteoarthritis [ 89 , 90 ], neurodegenerative diseases, and diabetes [ 100 ]. Due to this technique, it can become possible to generate healthy heart muscle cells and later transplant them to patients with heart disease.

Stem cell experiments on animals. These experiments are one of the many procedures that proved stem cells to be a crucial factor in future regenerative medicine

In the case of type 1 diabetes, insulin-producing cells in the pancreas are destroyed due to an autoimmunological reaction. As an alternative to transplantation therapy, it can be possible to induce stem cells to differentiate into insulin-producing cells [ 101 ].

Stem cells and tissue banks

iPS cells with their theoretically unlimited propagation and differentiation abilities are attractive for the present and future sciences. They can be stored in a tissue bank to be an essential source of human tissue used for medical examination. The problem with conventional differentiated tissue cells held in the laboratory is that their propagation features diminish after time. This does not occur in iPSCs.

The umbilical cord is known to be rich in mesenchymal stem cells. Due to its cryopreservation immediately after birth, its stem cells can be successfully stored and used in therapies to prevent the future life-threatening diseases of a given patient.

Stem cells of human exfoliated deciduous teeth (SHED) found in exfoliated deciduous teeth has the ability to develop into more types of body tissues than other stem cells [ 102 ] (Table  1 ). Techniques of their collection, isolation, and storage are simple and non-invasive. Among the advantages of banking, SHED cells are:

Guaranteed donor-match autologous transplant that causes no immune reaction and rejection of cells [ 103 ]

Simple and painless for both child and parent

Less than one third of the cost of cord blood storage

Not subject to the same ethical concerns as embryonic stem cells [ 104 ]

In contrast to cord blood stem cells, SHED cells are able to regenerate into solid tissues such as connective, neural, dental, or bone tissue [ 105 , 106 ]

SHED can be useful for close relatives of the donor

Fertility diseases

In 2011, two researchers, Katsuhiko Hayashi et al. [ 107 ], showed in an experiment on mice that it is possible to form sperm from iPSCs. They succeeded in delivering healthy and fertile pups in infertile mice. The experiment was also successful for female mice, where iPSCs formed fully functional eggs .

Young adults at risk of losing their spermatogonial stem cells (SSC), mostly cancer patients, are the main target group that can benefit from testicular tissue cryopreservation and autotransplantation. Effective freezing methods for adult and pre-pubertal testicular tissue are available [ 108 ].

Qiuwan et al. [ 109 ] provided important evidence that human amniotic epithelial cell (hAEC) transplantation could effectively improve ovarian function by inhibiting cell apoptosis and reducing inflammation in injured ovarian tissue of mice, and it could be a promising strategy for the management of premature ovarian failure or insufficiency in female cancer survivors.

For now, reaching successful infertility treatments in humans appears to be only a matter of time, but there are several challenges to overcome. First, the process needs to have high efficiency; second, the chances of forming tumours instead of eggs or sperm must be maximally reduced. The last barrier is how to mature human sperm and eggs in the lab without transplanting them to in vivo conditions, which could cause either a tumour risk or an invasive procedure.

Therapy for incurable neurodegenerative diseases

Thanks to stem cell therapy, it is possible not only to delay the progression of incurable neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease (AD), and Huntington disease, but also, most importantly, to remove the source of the problem. In neuroscience, the discovery of neural stem cells (NSCs) has nullified the previous idea that adult CNS were not capable of neurogenesis [ 110 , 111 ]. Neural stem cells are capable of improving cognitive function in preclinical rodent models of AD [ 112 , 113 , 114 ]. Awe et al. [ 115 ] clinically derived relevant human iPSCs from skin punch biopsies to develop a neural stem cell-based approach for treating AD. Neuronal degeneration in Parkinson’s disease (PD) is focal, and dopaminergic neurons can be efficiently generated from hESCs. PD is an ideal disease for iPSC-based cell therapy [ 116 ]. However, this therapy is still in an experimental phase ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4539501 /). Brain tissue from aborted foetuses was used on patients with Parkinson’s disease [ 117 ]. Although the results were not uniform, they showed that therapies with pure stem cells are an important and achievable therapy.

Stem cell use in dentistry

Teeth represent a very challenging material for regenerative medicine. They are difficult to recreate because of their function in aspects such as articulation, mastication, or aesthetics due to their complicated structure. Currently, there is a chance for stem cells to become more widely used than synthetic materials. Teeth have a large advantage of being the most natural and non-invasive source of stem cells.

For now, without the use of stem cells, the most common periodontological treatments are either growth factors, grafts, or surgery. For example, there are stem cells in periodontal ligament [ 118 , 119 ], which are capable of differentiating into osteoblasts or cementoblasts, and their functions were also assessed in neural cells [ 120 ]. Tissue engineering is a successful method for treating periodontal diseases. Stem cells of the root apical areas are able to recreate periodontal ligament. One of the possible methods of tissue engineering in periodontology is gene therapy performed using adenoviruses-containing growth factors [ 121 ].

As a result of animal studies, dentin regeneration is an effective process that results in the formation of dentin bridges [ 122 ].

Enamel is more difficult to regenerate than dentin. After the differentiation of ameloblastoma cells into the enamel, the former is destroyed, and reparation is impossible. Medical studies have succeeded in differentiating bone marrow stem cells into ameloblastoma [ 123 ].

Healthy dental tissue has a high amount of regular stem cells, although this number is reduced when tissue is either traumatized or inflamed [ 124 ]. There are several dental stem cell groups that can be isolated (Fig.  7 ).

Localization of stem cells in dental tissues. Dental pulp stem cells (DPSCs) and human deciduous teeth stem cells (SHED) are located in the dental pulp. Periodontal ligaments stem cells are located in the periodontal ligament. Apical papilla consists of stem cells from the apical papilla (SCAP)

Dental pulp stem cell (DPSC)

These were the first dental stem cells isolated from the human dental pulp, which were [ 125 ] located inside dental pulp (Table  2 ). They have osteogenic and chondrogenic potential. Mesenchymal stem cells (MSCs) of the dental pulp, when isolated, appear highly clonogenic; they can be isolated from adult tissue (e.g. bone marrow, adipose tissue) and foetal (e.g. umbilical cord) [ 126 ] tissue, and they are able to differentiate densely [ 127 ]. MSCs differentiate into odontoblast-like cells and osteoblasts to form dentin and bone. Their best source locations are the third molars [ 125 ]. DPSCs are the most useful dental source of tissue engineering due to their easy surgical accessibility, cryopreservation possibility, increased production of dentin tissues compared to non-dental stem cells, and their anti-inflammatory abilities. These cells have the potential to be a source for maxillofacial and orthopaedic reconstructions or reconstructions even beyond the oral cavity. DPSCs are able to generate all structures of the developed tooth [ 128 ]. In particular, beneficial results in the use of DPSCs may be achieved when combined with other new therapies, such as periodontal tissue photobiomodulation (laser stimulation), which is an efficient technique in the stimulation of proliferation and differentiation into distinct cell types [ 129 ]. DPSCs can be induced to form neural cells to help treat neurological deficits.

Stem cells of human exfoliated deciduous teeth (SHED) have a faster rate of proliferation than DPSCs and differentiate into an even greater number of cells, e.g. other mesenchymal and non-mesenchymal stem cell derivatives, such as neural cells [ 130 ]. These cells possess one major disadvantage: they form a non-complete dentin/pulp-like complex in vivo. SHED do not undergo the same ethical concerns as embryonic stem cells. Both DPSCs and SHED are able to form bone-like tissues in vivo [ 131 ] and can be used for periodontal, dentin, or pulp regeneration. DPSCs and SHED can be used in treating, for example, neural deficits [ 132 ]. DPSCs alone were tested and successfully applied for alveolar bone and mandible reconstruction [ 133 ].

Periodontal ligament stem cells (PDLSCs)

These cells are used in periodontal ligament or cementum tissue regeneration. They can differentiate into mesenchymal cell lineages to produce collagen-forming cells, adipocytes, cementum tissue, Sharpey’s fibres, and osteoblast-like cells in vitro. PDLSCs exist both on the root and alveolar bone surfaces; however, on the latter, these cells have better differentiation abilities than on the former [ 134 ]. PDLSCs have become the first treatment for periodontal regeneration therapy because of their safety and efficiency [ 135 , 136 ].

Stem cells from apical papilla (SCAP)

These cells are mesenchymal structures located within immature roots. They are isolated from human immature permanent apical papilla. SCAP are the source of odontoblasts and cause apexogenesis. These stem cells can be induced in vitro to form odontoblast-like cells, neuron-like cells, or adipocytes. SCAP have a higher capacity of proliferation than DPSCs, which makes them a better choice for tissue regeneration [ 137 , 138 ].

Dental follicle stem cells (DFCs)

These cells are loose connective tissues surrounding the developing tooth germ. DFCs contain cells that can differentiate into cementoblasts, osteoblasts, and periodontal ligament cells [ 139 , 140 ]. Additionally, these cells proliferate after even more than 30 passages [ 141 ]. DFCs are most commonly extracted from the sac of a third molar. When DFCs are combined with a treated dentin matrix, they can form a root-like tissue with a pulp-dentin complex and eventually form tooth roots [ 141 ]. When DFC sheets are induced by Hertwig’s epithelial root sheath cells, they can produce periodontal tissue; thus, DFCs represent a very promising material for tooth regeneration [ 142 ].

Pulp regeneration in endodontics

Dental pulp stem cells can differentiate into odontoblasts. There are few methods that enable the regeneration of the pulp.

The first is an ex vivo method. Proper stem cells are grown on a scaffold before they are implanted into the root channel [ 143 ].

The second is an in vivo method. This method focuses on injecting stem cells into disinfected root channels after the opening of the in vivo apex. Additionally, the use of a scaffold is necessary to prevent the movement of cells towards other tissues. For now, only pulp-like structures have been created successfully.

Methods of placing stem cells into the root channel constitute are either soft scaffolding [ 144 ] or the application of stem cells in apexogenesis or apexification. Immature teeth are the best source [ 145 ]. Nerve and blood vessel network regeneration are extremely vital to keep pulp tissue healthy.

The potential of dental stem cells is mainly regarding the regeneration of damaged dentin and pulp or the repair of any perforations; in the future, it appears to be even possible to generate the whole tooth. Such an immense success would lead to the gradual replacement of implant treatments. Mandibulary and maxillary defects can be one of the most complicated dental problems for stem cells to address.

Acquiring non-dental tissue cells by dental stem cell differentiation

In 2013, it was reported that it is possible to grow teeth from stem cells obtained extra-orally, e.g. from urine [ 146 ]. Pluripotent stem cells derived from human urine were induced and generated tooth-like structures. The physical properties of the structures were similar to natural ones except for hardness [ 127 ]. Nonetheless, it appears to be a very promising technique because it is non-invasive and relatively low-cost, and somatic cells can be used instead of embryonic cells. More importantly, stem cells derived from urine did not form any tumours, and the use of autologous cells reduces the chances of rejection [ 147 ].

Use of graphene in stem cell therapy

Over recent years, graphene and its derivatives have been increasingly used as scaffold materials to mediate stem cell growth and differentiation [ 148 ]. Both graphene and graphene oxide (GO) represent high in-plane stiffness [ 149 ]. Because graphene has carbon and aromatic network, it works either covalently or non-covalently with biomolecules; in addition to its superior mechanical properties, graphene offers versatile chemistry. Graphene exhibits biocompatibility with cells and their proper adhesion. It also tested positively for enhancing the proliferation or differentiation of stem cells [ 148 ]. After positive experiments, graphene revealed great potential as a scaffold and guide for specific lineages of stem cell differentiation [ 150 ]. Graphene has been successfully used in the transplantation of hMSCs and their guided differentiation to specific cells. The acceleration skills of graphene differentiation and division were also investigated. It was discovered that graphene can serve as a platform with increased adhesion for both growth factors and differentiation chemicals. It was also discovered that π-π binding was responsible for increased adhesion and played a crucial role in inducing hMSC differentiation [ 150 ].

Therapeutic potential of extracellular vesicle-based therapies

Extracellular vesicles (EVs) can be released by virtually every cell of an organism, including stem cells [ 151 ], and are involved in intercellular communication through the delivery of their mRNAs, lipids, and proteins. As Oh et al. [ 152 ] prove, stem cells, together with their paracrine factors—exosomes—can become potential therapeutics in the treatment of, e.g. skin ageing. Exosomes are small membrane vesicles secreted by most cells (30–120 nm in diameter) [ 153 ]. When endosomes fuse with the plasma membrane, they become exosomes that have messenger RNAs (mRNAs) and microRNAs (miRNAs), some classes of non-coding RNAs (IncRNAs) and several proteins that originate from the host cell [ 154 ]. IncRNAs can bind to specific loci and create epigenetic regulators, which leads to the formation of epigenetic modifications in recipient cells. Because of this feature, exosomes are believed to be implicated in cell-to-cell communication and the progression of diseases such as cancer [ 155 ]. Recently, many studies have also shown the therapeutic use of exosomes derived from stem cells, e.g. skin damage and renal or lung injuries [ 156 ].

In skin ageing, the most important factor is exposure to UV light, called “photoageing” [ 157 ], which causes extrinsic skin damage, characterized by dryness, roughness, irregular pigmentation, lesions, and skin cancers. In intrinsic skin ageing, on the other hand, the loss of elasticity is a characteristic feature. The skin dermis consists of fibroblasts, which are responsible for the synthesis of crucial skin elements, such as procollagen or elastic fibres. These elements form either basic framework extracellular matrix constituents of the skin dermis or play a major role in tissue elasticity. Fibroblast efficiency and abundance decrease with ageing [ 158 ]. Stem cells can promote the proliferation of dermal fibroblasts by secreting cytokines such as platelet-derived growth factor (PDGF), transforming growth factor β (TGF-β), and basic fibroblast growth factor. Huh et al. [ 159 ] mentioned that a medium of human amniotic fluid-derived stem cells (hAFSC) positively affected skin regeneration after longwave UV-induced (UVA, 315–400 nm) photoageing by increasing the proliferation and migration of dermal fibroblasts. It was discovered that, in addition to the induction of fibroblast physiology, hAFSC transplantation also improved diseases in cases of renal pathology, various cancers, or stroke [ 160 , 161 ].

Oh [ 162 ] also presented another option for the treatment of skin wounds, either caused by physical damage or due to diabetic ulcers. Induced pluripotent stem cell-conditioned medium (iPSC-CM) without any animal-derived components induced dermal fibroblast proliferation and migration.

Natural cutaneous wound healing is divided into three steps: haemostasis/inflammation, proliferation, and remodelling. During the crucial step of proliferation, fibroblasts migrate and increase in number, indicating that it is a critical step in skin repair, and factors such as iPSC-CM that impact it can improve the whole cutaneous wound healing process. Paracrine actions performed by iPSCs are also important for this therapeutic effect [ 163 ]. These actions result in the secretion of cytokines such as TGF-β, interleukin (IL)-6, IL-8, monocyte chemotactic protein-1 (MCP-1), vascular endothelial growth factor (VEGF), platelet-derived growth factor-AA (PDGF-AA), and basic fibroblast growth factor (bFGF). Bae et al. [ 164 ] mentioned that TGF-β induced the migration of keratinocytes. It was also demonstrated that iPSC factors can enhance skin wound healing in vivo and in vitro when Zhou et al. [ 165 ] enhanced wound healing, even after carbon dioxide laser resurfacing in an in vivo study.

Peng et al. [ 166 ] investigated the effects of EVs derived from hESCs on in vitro cultured retinal glial, progenitor Müller cells, which are known to differentiate into retinal neurons. EVs appear heterogeneous in size and can be internalized by cultured Müller cells, and their proteins are involved in the induction and maintenance of stem cell pluripotency. These stem cell-derived vesicles were responsible for the neuronal trans-differentiation of cultured Müller cells exposed to them. However, the research article points out that the procedure was accomplished only on in vitro acquired retina.

Challenges concerning stem cell therapy

Although stem cells appear to be an ideal solution for medicine, there are still many obstacles that need to be overcome in the future. One of the first problems is ethical concern.

The most common pluripotent stem cells are ESCs. Therapies concerning their use at the beginning were, and still are, the source of ethical conflicts. The reason behind it started when, in 1998, scientists discovered the possibility of removing ESCs from human embryos. Stem cell therapy appeared to be very effective in treating many, even previously incurable, diseases. The problem was that when scientists isolated ESCs in the lab, the embryo, which had potential for becoming a human, was destroyed (Fig.  8 ). Because of this, scientists, seeing a large potential in this treatment method, focused their efforts on making it possible to isolate stem cells without endangering their source—the embryo.

Use of inner cell mass pluripotent stem cells and their stimulation to differentiate into desired cell types

For now, while hESCs still remain an ethically debatable source of cells, they are potentially powerful tools to be used for therapeutic applications of tissue regeneration. Because of the complexity of stem cell control systems, there is still much to be learned through observations in vitro. For stem cells to become a popular and widely accessible procedure, tumour risk must be assessed. The second problem is to achieve successful immunological tolerance between stem cells and the patient’s body. For now, one of the best ideas is to use the patient’s own cells and devolve them into their pluripotent stage of development.

New cells need to have the ability to fully replace lost or malfunctioning natural cells. Additionally, there is a concern about the possibility of obtaining stem cells without the risk of morbidity or pain for either the patient or the donor. Uncontrolled proliferation and differentiation of cells after implementation must also be assessed before its use in a wide variety of regenerative procedures on living patients [ 167 ].

One of the arguments that limit the use of iPSCs is their infamous role in tumourigenicity. There is a risk that the expression of oncogenes may increase when cells are being reprogrammed. In 2008, a technique was discovered that allowed scientists to remove oncogenes after a cell achieved pluripotency, although it is not efficient yet and takes a longer amount of time. The process of reprogramming may be enhanced by deletion of the tumour suppressor gene p53, but this gene also acts as a key regulator of cancer, which makes it impossible to remove in order to avoid more mutations in the reprogrammed cell. The low efficiency of the process is another problem, which is progressively becoming reduced with each year. At first, the rate of somatic cell reprogramming in Yamanaka’s study was up to 0.1%. The use of transcription factors creates a risk of genomic insertion and further mutation of the target cell genome. For now, the only ethically acceptable operation is an injection of hESCs into mouse embryos in the case of pluripotency evaluation [ 168 ].

Stem cell obstacles in the future

Pioneering scientific and medical advances always have to be carefully policed in order to make sure they are both ethical and safe. Because stem cell therapy already has a large impact on many aspects of life, it should not be treated differently.

Currently, there are several challenges concerning stem cells. First, the most important one is about fully understanding the mechanism by which stem cells function first in animal models. This step cannot be avoided. For the widespread, global acceptance of the procedure, fear of the unknown is the greatest challenge to overcome.

The efficiency of stem cell-directed differentiation must be improved to make stem cells more reliable and trustworthy for a regular patient. The scale of the procedure is another challenge. Future stem cell therapies may be a significant obstacle. Transplanting new, fully functional organs made by stem cell therapy would require the creation of millions of working and biologically accurate cooperating cells. Bringing such complicated procedures into general, widespread regenerative medicine will require interdisciplinary and international collaboration.

The identification and proper isolation of stem cells from a patient’s tissues is another challenge. Immunological rejection is a major barrier to successful stem cell transplantation. With certain types of stem cells and procedures, the immune system may recognize transplanted cells as foreign bodies, triggering an immune reaction resulting in transplant or cell rejection.

One of the ideas that can make stem cells a “failsafe” is about implementing a self-destruct option if they become dangerous. Further development and versatility of stem cells may cause reduction of treatment costs for people suffering from currently incurable diseases. When facing certain organ failure, instead of undergoing extraordinarily expensive drug treatment, the patient would be able to utilize stem cell therapy. The effect of a successful operation would be immediate, and the patient would avoid chronic pharmacological treatment and its inevitable side effects.

Although these challenges facing stem cell science can be overwhelming, the field is making great advances each day. Stem cell therapy is already available for treating several diseases and conditions. Their impact on future medicine appears to be significant.

After several decades of experiments, stem cell therapy is becoming a magnificent game changer for medicine. With each experiment, the capabilities of stem cells are growing, although there are still many obstacles to overcome. Regardless, the influence of stem cells in regenerative medicine and transplantology is immense. Currently, untreatable neurodegenerative diseases have the possibility of becoming treatable with stem cell therapy. Induced pluripotency enables the use of a patient’s own cells. Tissue banks are becoming increasingly popular, as they gather cells that are the source of regenerative medicine in a struggle against present and future diseases. With stem cell therapy and all its regenerative benefits, we are better able to prolong human life than at any time in history.

Abbreviations

Basic fibroblast growth factor

Bone morphogenic proteins

Dental follicle stem cells

Dental pulp stem cells

Embryonic bodies

Embryonic stem cells

Fibroblast growth factors

Good Manufacturing Practice

Graphene oxide

Human amniotic fluid-derived stem cells

Human embryonic stem cells

Human foreskin fibroblasts

Inner cell mass

Non-coding RNA

Induced pluripotent stem cells

In vitro fertilization

Knockout serum replacement

Leukaemia inhibitory factor

Monocyte chemotactic protein-1

Fibroblasts

Messenger RNA

Mesenchymal stem cells of dental pulp

Myogenic differentiation

Osteoarthritis

Octamer-binding transcription factor 3 and 4

Platelet-derived growth factor

Platelet-derived growth factor-AA

Periodontal ligament stem cells

Rho-associated protein kinase

Stem cells from apical papilla

Stem cells of human exfoliated deciduous teeth

Synthetic Serum Substitute

Trophectoderm

Vascular endothelial growth factor

Transforming growth factors

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Zakrzewski, W., Dobrzyński, M., Szymonowicz, M. et al. Stem cells: past, present, and future. Stem Cell Res Ther 10 , 68 (2019). https://doi.org/10.1186/s13287-019-1165-5

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Paul L Wolf, George Liggins, Dan Mercola, The Cloning Debates and Progress in Biotechnology, Clinical Chemistry , Volume 43, Issue 11, 1 November 1997, Pages 2019–2020, https://doi.org/10.1093/clinchem/43.11.2019

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The perception by humans of what is doable is itself a great determiner of future events. Thus, the successful sheep cloning experiment leading to “Dolly” by Ian Wilmut and associates at Roslin Institute, Midlothian, UK, compels us to look in the mirror and consider the issue of human cloning. Should it occur, and if not, how should that opposing mandate be managed? If human cloning should have an acceptable role, what is that role and how should it be monitored and supervised?

In the February 27, 1997, issue of Nature , Ian Wilmut et al. reported that they cloned a sheep (which they named “Dolly”) by transferring the nuclear DNA from an adult sheep udder cell into an egg whose DNA had been removed ( 1 ). Their cloning experiments have led to widespread debate on the potential application of this remarkable technique to the cloning of humans. Following the Scottish researchers’ startling report, President Clinton declared his opposition to using this technique to clone humans. He moved swiftly to order that federal funds not be used for such an experiment and asked an independent panel of experts, the National Bioethics Advisory Commission (NBAC), chaired by Princeton University President Harold Shapiro, to report to the White House with recommendations for a national policy on human cloning. According to recommendations by the NBAC, human cloning is likely to become a crime in the US in the near future. The Commission’s main recommendation is to enact federal legislation to prohibit any attempts, whether in a research or a clinical setting, to create a human through somatic cell nuclear transfer cloning.

The concept of genetic manipulation is not new and has been a general practice for more than a century, through practices ranging from selective cross-pollination in plants to artificial insemination in domestic farm animals.

Wilmut and his colleagues made 277 attempts before they succeeded with Dolly. Previously, investigators had reported successful cloning in frogs, mice, and cattle ( 2 )( 3 )( 4 )( 5 ), and 1 week after Wilmut’s report, Don Wolf and colleagues at the Oregon Regional Primate Research Center reported their cloning of two rhesus monkeys by utilizing embryonic cells. The achievement of Wilmut’s team shocked nucleic acid experts, who thought it would be an impossible feat. They believed that the DNA of adult cells could not perform similarly to the DNA formed when a spermatozoa’s genes mingle with those of an ovum.

On July 25, 1997, the Roslin team also reported the production of lambs that contained human genes ( 6 ). Utilizing techniques similar to those they had used in Dolly, they inserted a human gene into the nuclei of sheep cells. These cells were next inserted into the ova of sheep from which the DNA had been removed. The resulting lambs contained the human gene in every cell. In this new procedure the DNA had been inserted into skin fibroblast cells, which are specialized cells, unlike previous procedures in which DNA was introduced into a fertilized ovum. The new lamb has been named “Polly” because she is a Poll Dorset sheep. The goal of this new genetically engineered lamb is for these lambs to produce human proteins necessary for the treatment of human genetic diseases, such as factor VIII for hemophiliacs, cystic fibrosis transmembrane conductance regulator (CFTR) substance for patients with cystic fibrosis, tissue plasminogen activator to induce lysis of acute coronary and cerebral artery thrombi, and human growth factor.

Charles Darwin was frightened when he concluded that humans were not specifically separated from all other animals. Not until 20 years after his discovery did he have the courage to publish his findings, which changed the way humans view life on earth. Wilmut’s amazing investigations have also created worldwide fear, misunderstanding, and ethical shock waves. Politicians and a few scientists are proposing legislation to outlaw human cloning ( 7 ). Although the accomplishment of cloning clearly could provide many benefits to medicine and to conservation of endangered species of animals, politicians and a few scientists fear that the cloning procedure will be abused.

The advantages of cloning are numerous. The ability to clone dairy cattle may have a larger impact on the dairy industry than artificial insemination. Cloning might be utilized to produce multiple copies of animals that are especially good at producing meat, milk, or wool. The average cow makes 13 000 pounds (5800 kg) of milk a year. Cloning of cows that are superproducers of milk might result in cows producing 40 000 pounds (18 000 kg) of milk a year.

Wilmut’s recent success in cloning “Polly” represents his main interest in cloning ( 8 ). He believes in cloning animals able to produce proteins that are or may prove to be useful in medicine. Cloned female animals could produce large amounts of various important proteins in their milk, resulting in female animals that serve as living drug factories. Investigators might be able to clone animals affected with human diseases, e.g., cystic fibrosis, and investigate new therapies for the human diseases expressed by these animals.

Another possibility of cloning could be to change the proteins on the cell surface of heart, liver, kidney, or lung, i.e., to produce organs resembling human organs and enhancing the supply of organs for human transplantation. The altered donor organs, e.g., from pigs, would be less subject to rejection by the human recipient. The application of cloning in the propagation of endangered species and conservation of gene pools has been proposed as another important use of the cloning technique ( 9 )( 10 ).

The opponents of cloning have especially focused on banning the cloning of humans ( 11 ). The UK, Australia, Spain, Germany, and Denmark have implemented laws barring human cloning. Opponents of human cloning have cited potential ethical and legal implications. They emphasize that individuals are more than a sum of their genes. A clone of an individual might have a different environment and thus might be a different person psychologically and have a different “soul.” Cloning of a human is replication and not procreation.

Morally questionable uses of genetic material transfer and cloning obviously exist. For example, infertility experts might be especially interested in the cloning technique to produce identical twins, triplets, or quadruplets. Parents of a child who has a terminal illness might wish to have a clone of the child to replace the dying child. The old stigma, eugenics, also raises its ugly head if infertile couples wish to use the nuclear transfer techniques to ensure that their “hard-earned” offspring will possess excellent genes. Moral perspectives will differ tremendously in these cases. Judgments about the appropriateness of such uses are outside the realm of science.

Opponents of animal cloning are concerned that cloning will negate genetic diversity of livestock. This also applies to human cloning, which could negate genetic diversity of humans. Cloning creates, by definition, a second class of human, a human with a determined genotype called into existence, however benevolently, at the behest of another. The insulation of selection-of-mate is lost, and the second class is created. Few contrasts could be so clear. Selection-of-mate is so imprecise that, at present, would-be parents have to accept a complete new genome for the sake of including or excluding one or a few traits; cloning, in contrast, is the precise determination of all genes. If we acknowledge that the creation of a second class of humans is unethical, then we preempt any argument that some motivations for human cloning may be acceptable.

The opponents of cloning also fear that biotechnically cloned foods might increase the risk of humans acquiring some malignancies or infections such as “mad cow disease,” a prion spongiform dementia encephalopathy (human Jakob–Creutzfeldt disease).

The technological advances associated with manipulation of genetic materials now permit us to envision replacement of defective genes with “good” genes. Although current progress is not sufficient to make this practical today for human diseases, any efforts to stop such research as a result of cloning hysteria would preclude the development of true cures for many hereditary human diseases. Unreasonable restrictions on the use of human tissues in gene transfer research will have the inevitable consequences of delaying, if not preventing, the development of strategies to combat defective genes.

Wise legislation will enable humankind to realize the benefits of gene transfer technologies without risking the horrors that could arise from misuse of these technologies. Our hope is that such wise legislation is what will be enacted. In our view, the controversy surrounding human cloning must not lead to prohibitions that would prevent advances similar to those described here.

Wilmut I, Schnieke AE, McWhire J, Kind AJ, Campbell KHS. Viable offspring derived from fetal and adult mammalian cells. Nature 1997 ; 385 : 810 -813.

Pennisi E, Williams N. Will Dolly send in the clones?. Science 1997 ; 275 : 1415 -1416.

Gurdon JB, Laskey RA, Reeves OR. The developmental capacity of nuclei transplanted from keratinized skin cells of adult frogs. J Embryol Exp Morphol 1975 ; 34 : 93 -112.

Prather RS. Nuclei transplantation in the bovine embryo. Assessment of donor nuclei and recipient oocyte. Biol Reprod 1987 ; 37 : 859 -866.

Kwon OY, Kono T. Production of identical sextuplet mice by transferring metaphase nuclei from 4-cell embryos. J Reprod Fert Abst Ser 1996 ; 17 : 30 .

Kolata G. Lab yields lamb with human gene. NY Times 1997;166:July 25;A12..

Specter M, Kolta G. After decades of missteps, how cloning succeeded. NY Times 1997;166:March 3;B6–8..

Ibrahim YM. Ian Wilmut. NY Times 1997;166:February 24;B8..

Ryder OA, Benirschke K. The potential use of “cloning” in the conservation effort. Zoo Biol 1997 ; 16 : 295 -300.

Cohen J. Can cloning help save beleaguered species?. Science 1997 ; 276 : 1329 -1330.

Williams N. Cloning sparks calls for new laws. Science 1997;275:141-5..

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Cloning articles from across Nature Portfolio

Cloning is a method that is used to produce genetically identical copies of pieces of DNA, cells or organisms. Cloning methods include: molecular cloning, which makes copies of pieces of DNA; cellular cloning, which makes copies of a cell; and whole organism cloning. All cloning methods involve DNA and cell manipulation.

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Somatic cloning of rhesus monkey has not been successful until now. Here, authors report epigenetic abnormalities in SCNT embryos and placentas and develop a trophoblast replacement method that enables them to successful clone of a healthy male rhesus monkey.

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Haploidy in somatic cells is induced by mature oocytes in mice

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Scientists Clone Human Embryos To Make Stem Cells

Michaeleen Doucleff

A scientist removes the nucleus from a human egg using a pipette. This is the first step to making personalized embryonic stem cells. Courtesy of OHSU Photos hide caption

A scientist removes the nucleus from a human egg using a pipette. This is the first step to making personalized embryonic stem cells.

Scientists say they have, for the first time, cloned human embryos capable of producing embryonic stem cells.

The accomplishment is a long-sought step toward harnessing the potential power of embryonic stem cells to treat many human diseases. But the work also raises a host of ethical concerns.

"This is a huge scientific advance," said Dr. George Daley , a Harvard stem cell scientist who wasn't involved in the work. "But it's going to, I think, raise the specter of controversy again."

The controversy arises from several factors. The experiments involve creating and then destroying human embryos for research purposes, which some find morally repugnant. The scientists also used cloning techniques, which raise concerns that the research could lead to the cloning of people.

Ever since human embryonic stem cells were discovered, scientists have had high hopes for them because the cells can morph into any kind of cell in the body. That ability means, in theory, that they could be used eventually to treat all sorts of illnesses, including diabetes, Alzheimer's, Parkinson's and spinal cord injuries.

So for years, scientists have been trying to use cloning techniques to make embryonic stem cells that are essentially a genetic match for patients. The idea is that such a close match would prevent their bodies from rejecting the cells.

"It's been a holy grail that we've been after for years," says Dr. John Gearhart , a stem cell pioneer at the University of Pennsylvania.

But every previous attempt ended in failure or fraud, leading many scientists to wonder if the goal might be impossible to reach.

Making Personalized Stem Cells

Scientists report Wednesday that they have successfully cloned human embryos from a person's skin cells. Here's how they could eventually use the technology to create new therapies for a patient.

Source: Mitalipov Lab/OHSU

Credit: Adapted for NPR by Alyson Hurt

However, Shoukhrat Mitalipov of the Oregon Health & Science University and his colleagues never gave up. They succeeded in mice and monkeys. And in this week's issue of the journal Cell , Mitalipov's team reports they finally did it in humans.

"I'm very excited," Mitalipov says. "It's a very significant advance."

The researchers first recruited women who were willing to provide eggs for the research. Next, they removed most of the DNA from each egg and replaced the genetic material with DNA from other peoples' skin cells.

Then, after a long search, they finally found the best way to stimulate each egg so that it would develop into an embryo without the need to be fertilized with sperm. The key turned out to be a combination of chemicals and an electric pulse.

"We had to find the perfect combination," Mitalipov says. As it turned out, that perfect combination included something surprising: caffeine.

"The Starbucks experiment, I guess," quipped Daley. "This little change in the cocktail was what really allowed the experiment to really ultimately succeed."

Shoukhrat Mitalipov, of Oregon Health & Science University, first cloned monkey embryos before trying his method on human eggs. Courtesy of OHSU Photos hide caption

Shoukhrat Mitalipov, of Oregon Health & Science University, first cloned monkey embryos before trying his method on human eggs.

That ingredient, plus other tweaks in the process, including using fresh eggs and determining the optimal stage of each egg's development, Mitalipov says.

The researchers showed that the resulting embryos could develop to a stage where they could produce healthy stem cells containing the genes from the skin cells. They even showed that the stem cells could be turned into other types of cells, including heart cells that in a laboratory dish could pulse like a beating heart.

The work drew immediate criticism because of ethical concerns.

First of all, the Oregon researchers compensated women financially to donate eggs for the experiments — something many in the field have considered ethically questionable.

But beyond that, the creation and destruction of a human embryo is morally repugnant to people who believe an embryo has the same moral standing as a human being.

"This is a case in which one is deliberately setting out to create a human being for the sole purpose of destroying that human being," says Dr. Daniel Sulmasy , a professor of medicine and a bioethicist at the University of Chicago. "I'm of the school that thinks that that's morally wrong no matter how much good could come of it."

Moreover, Mitalipov used the same method that researchers used previously to clone Dolly the sheep . That approach raises the possibility that scientists could try to clone a human being.

"This raises serious problems because it is the first actual human cloning," Sulmasy says. "We already know there are people out there who are itching to be able to be the first to bring a cloned human being to birth. And I think it's going to happen."

But Mitalipov dismisses those concerns. He says the embryos he created aren't the equivalent of a human being because they weren't fertilized naturally. And his experiments with monkeys indicate that it's unlikely that they could ever develop into a healthy baby.

"The procedures we developed actually are very efficient to make stem cells, but it's unlikely that this will be very useful for kind of reproductive cloning," Mitalipov says.

Other researchers agree with him and argue that the possible benefits of the research outweigh the concerns. "Where you can improve [a patient's] quality of life tremendously through this kind of technology, I personally believe that it is ethical to use material like this," Gearhart says.

The scientists acknowledge that it will be years before anyone knows whether this step will actually result in treatments that might help patients. In the meantime, it's clear that the intense debate over embryonic stem cells is far from over.

• embryonic stem cells

Our experiences have told us that, with a little work, we humans can clone just about anything we want, from frogs to sheep—and probably even ourselves.

So we can clone things. But why would we want to? Below are some of the ways in which cloning might be useful.

Cloning in Medicine

Cloning for medical purposes has the potential to benefit large numbers of people. How might cloning be used in medicine?

Cloning animal models of disease

Much of what researchers learn about human disease comes from studying animal models such as mice. Often, animal models are genetically engineered to carry disease-causing mutations in their genes. Creating these transgenic animals is a time-intensive process that requires trial-and-error and several generations of breeding. Cloning could help reduce the time needed to make a transgenic animal model, and the result would be a population of genetically identical animals for study.

Cloning to make stem cells

Stem cells build, maintain, and repair the body throughout our lives. Because these are processes that stem cells do naturally, they can be manipulated to repair damaged or diseased organs and tissues. But stem cells transferred from one person to another (such as in a bone marrow transplant) are seen as foreign, and they usually trigger an immune response.

Some researchers are looking at cloning as a way to create stem cells that are genetically identical to an individual. These cells could then be used for medical purposes, possibly even for growing whole organs. And stem cells cloned from someone with a disease could be grown in culture and studied to help researchers understand the disease and develop treatments.

In 2013, scientists at Oregon Health and Science University were the first to use cloning techniques to successfully create human embryonic stem cells. The donor DNA came from an 8-month-old with a rare genetic disease.

Find out more about Stem Cells .

Reviving Endangered or Extinct Species

You might have seen the Jurassic Park movies. In the original feature film, based on the Michael Crichton novel, scientists use DNA preserved for tens of millions of years to clone dinosaurs. They run into trouble, however, when they realize that the cloned creatures were smarter and fiercer than expected. Could we really clone dinosaurs?

In theory? Yes. You would need:

• A well-preserved source of DNA from the extinct dinosaur, and
• A closely related species, currently living, that could serve as an egg donor and surrogate mother.

In reality? Probably not.

It's extremely unlikely that dinosaur DNA could survive undamaged for such a long time. However, scientists have been working to clone species that became extinct more recently, using DNA from well-preserved tissue samples. A number of projects are underway to clone extinct species, including the wooly mammoth.

In 2009, scientists had their first near-success resurrecting an extinct animal. Using goats as egg donors and surrogates, they made several clones of a wild mountain goat called the bucardo—but the longest-surviving clone died soon after birth. Even if the effort eventually succeeds, the only frozen tissue sample comes from a female, so it will only produce female clones. However, scientists speculate they may beable to remove one X chromosome and add a Y chromosome from a related goat species to make a male.

Cloning endangered species is much easier, mainly because the surviving animals can donate healthy, living cells. In fact, several wild species have been cloned already, including two relatives of cattle called the guar and the banteng, mouflon sheep, deer, bison, and coyotes. However, some experts are skeptical that cloning can help a species recover. One big challenge endangered species face is the loss of genetic diversity, and cloning does nothing to address this problem. When a species has high genetic diversity, there is a better chance that some individuals would have genetic variations that could help them survive an environmental challenge such as an infectious disease. Cloning also does not address the problems that put the species in danger in the first place, such as habitat destruction and hunting. But cloning may be one more tool that conservation scientists can add to their toolbox.

Learn more about Conservation Genetics .

Left: the alpine ibex, a close cousin of the Bucardo. Right: the last remaining Bucardo with the research team before her eventual death. She was blindfolded to shield her eyes from the photographer's flash. Image courtesy of Advanced Cell Technology.

Reproducing a Deceased Pet

If you really wanted to, and if you had enough money, you could clone your beloved family cat. At least one biotechnology company in the United States has offered cat cloning services for the privileged and bereaved. But don't assume that your cloned kitty will be exactly the same as the one you know and love. An individual is a product of more than its genes—the environment plays an important role in shaping personality and many other traits.

On December 22, 2001, a kitten named CC made history as the first cat—and the first domestic pet—ever to be cloned. CC and Rainbow, the donor of CC's genetic material, are pictured at the right.

But do you notice something odd about this picture? If CC is a clone of Rainbow—an exact genetic copy—then why are they different colors?

The answer lies in the X chromosome. In cats, a gene that helps determine coat color resides on this chromosome. Both CC and Rainbow, being females, have two X chromosomes. (Males have one X and one Y chromosome.) Since the two cats have the exact same X chromosomes, they have the same two coat color genes, one specifying black and the other specifying orange.

Very early in her development, each of Rainbow's cells "turned off" oneentire X chromosome, thereby turning off either the black or the orange color gene. This process, called X-inactivation, happens normally in females, in order to prevent them from having twice as much X-chromosome activity as males. It also happens randomly, meaning that different cells turn off different X chromosomes.

So like all female mammals, Rainbow developed as a mosaic. Each cell that underwent X-inactivation gave rise to a patch of cells that had oneor the other coat color gene inactivated. Some patches specified black,other patches specified orange, and still others specified white, due to more complex genetic events. This is how all calico cats, like Rainbow, get their markings.

CC looks different because she was made from a somatic cell from Rainbow in which the X-chromosome with the orange gene had been inactivated; only the black gene was active. What's interesting is that, as CC developed, her cells did not change the inactivation pattern. Therefore, unlike Rainbow, CC developed without any cells that specified orange coat color. The result is CC's black and white tiger-tabby coat.

Left: CC (or Carbon Copy). Right: Rainbow. Photo courtesy TAMU, College of Veterinary Medicine.

Rainbow and CC are living proof that a clone will not look exactly like the donor of its genetic material.

Cloning livestock

Programs are underway to clone agricultural animals, such as cattle and pigs, that are efficient producers of high-quality milk or meat.

A group of researchers at Utah State University led by Dr. Ken White, Dean of College of Agriculture & Applied Science, have been able to clone steer from slaughterhouse carcasses. Their aim isn't to produce animals for consumption—cloning is far more labor-intensive and expensive than conventional breeding methods. Instead, they want to use these animals as breeding stock.

The important thing to know about beef cattle is that the quality and yield of their meat can be assessed only after they are slaughtered. And male animals are routinely neutered when they're a few days old. That is, their testes are removed, so they are unable to make sperm. But cells from a high-quality carcass can be cloned, giving rise to an animal that is able, though conventional breeding methods, to pass its superior genes to its offspring.

Scientists have also cloned mules, a reproductively sterile hybrid of a male donkey and a female horse; dairy cows; and horses. One gelded racing horse, a male whose testes have been removed, has a clone that is available for breeding. Some of the cloned cows produce about twice as much milk as the average producer. And a cloned racing mule is ranked among the best in the world.

Drug production

Farm animals such as cows, sheep, and goats are being genetically engineered to produce drugs or proteins that are useful in medicine. As an example, scientists could take cells from a cow that produces large amounts of milk and grow them in culture. Then they could insert a gene into the DNA of these cells that codes for a drug or a vaccine. If they take the nucleus from one of these cells and transfer it to a cow egg, it could develop into a cow that makes the drug in its milk. Since every cell in the cow would carry the drug gene, it could pass the gene to its offspring, creating a whole herd of drug-producing cows. Even better, we could avoid the issue of the genetic reshuffling that happensduring sexual reproduction and simply clone our drug-producing cow.

Cloning Humans

The prospect of cloning humans is highly controversial, and it raises a number of ethical, legal, and social challenges that need to be considered.

The vast majority of scientists and lawmakers view human reproductive cloning—cloning for the purpose of making a human baby—immoral. Supporters see it as a possible solution to infertility problems. Some even imagine making clones of geniuses, whose work could advance society. Far-fetched views describe farms filled with clones whose organs are harvested for transplantation—a truly horrific idea.

For now, risks and technical challenges—as well as laws that make it illegal—will probably keep human reproductive cloning from becoming a reality. Even though many species have been cloned successfully, the process is still technically difficult and inefficient. The success rate in cloning is quite low: most embryos fail to develop, and many pregnancies end in miscarriage.

Current efforts at human cloning are focused on creating embryonic stem cells for research and medicine, as described above. However, many feel that this type of therapeutic cloning comes dangerously close to human reproductive cloning. And once techniques become more streamlined and efficient, they fear that some may be tempted to take that next step.

From a technical and moral standpoint, before human cloning becomes routine, we need to have a good idea of the risks involved.

Cloning and Stem Cell

Human embryonic stem cells are stem cells that are derived from the developing human embryo. They are most useful in research because of their ability to change into any type of cell, tissue or organ in the human body – that is, their pluripotency. As such they can be used in the treatment of a very large number of conditions. The main ethical issues arise from their source – donated embryos, most often left over from the IVF process.

Non-embryonic stem cells are stem cells that are not derived from an embryo. Two examples of these are cord-blood stem cells and induced pluripotent stem cells. Because they are not derived from embryos there is substantially less moral controversy about the use of these stems cells in research. However, there are limits to the use of non-embryonic stem cells. First, for all but induced pluripotent stem cells, other stem cells are not as versatile as the embryonic version and so they cannot give rise to the same range of human cells; and second, they do not help with research that is aimed at understanding the developmental mechanisms involved in these processes.

Admixed human embryos are a range of ‘combined’ human-animal embryonic cells. The most commonly used in research are ‘cybrids’. Cybrids are made by inserting the nucleus of a human cell into an animal egg from which the nucleus has been removed. They are useful in research because they are an easy way to create embryos so that the understanding and control of human embryos and development can be understood. Chimeras are usually formed by merging human and animal embryos whilst hybrids have human and animal chromosomes. The most common objection to these techniques involves claims about interfering with nature – by creating ‘half-human, half-animals’. A further objection points to the lack of dignity associated with the creation of these embryos. Such an objection relies on a particular conception of the moral status of the embryo.

Therapeutic cloning is cloning that is aimed at producing stem cells, tissue or organs for the therapeutic use of the individual from whom they are cloned. The advantage of therapeutic cloning is that the stem cells or other tissue created will have matched DNA to the  recipient and so there will be little risk of tissue rejection. The main ethical issue associated with therapeutic cloning is that it requires the creation and destruction of an embryo, which on some views on the moral status of embryos is wrong.

Part-Human Chimera Research

The creation of part-human chimeric embryos and live-born chimeras could prove enormously beneficial as a tool for studying development and disease, testing therapeutic drugs, and generating tissues and organs for transplant.*

Chimeras are usually formed by merging human and animal embryos whilst hybrids have human and animal chromosomes. The most common objection to these techniques involves claims about interfering with nature – by creating ‘half-human, half-animals’. A further objection points to the lack of dignity associated with the creation of these embryos. Such an objection relies on a particular conception of the moral status of the embryo.**

On Thursday 15 April 2021, Professor Juan Carlos Izpisua Belmonte and his team announced in the journal Cell that they have injected human stem cells into monkey blastocytes, and succeeded in keeping some of the chimeric embryos alive for up to 20 days. It is hoped that by studying the 'crosstalk' between the monkey and human cells, it will soon be possible to generate human organs in different species that could help alleviate the worldwide shortage of organs for transplantation.

Full paper: Tao Tan, Jun Wu, Chenyang Si, et al, (2021), ' Chimeric contribution of human extended pluripotent stem cells to monkey embryos ex vivo ', Cell , VOLUME 184, ISSUE 8, P2020-2032.E14, APRIL 15, 2021

*For an overview of the key ethical issues raised by part-human chimera research, and of possible regulatory approaches which may address these issues, see Julian Koplin and Julian Savulescu's article ' Time to rethink the law on part-human chimeras '.

**OUC's Katrien Devolder, Lauren Yip and Tom Douglas discuss the moral status of chimera, and the ethical issues surrounding such research in their freely available 2020 paper ' The Ethics of Creating and Using Human-Animal Chimeras ',  The ILAR Journal , Volume 60, Issue 3, Pages 434–438 [ download author pre-print PDF ]

Press Release

Response to the isscr guidelines for stem cell research and clinical translation.

Published May 26, 2021 | By César Palacios-González

“The new ISSCR guidelines provide a much welcomed framework for research that many find ethically contentious.

Genome editing, the creation of human gametes in a lab, and the creation of human/non-human chimeras raise fundamental ethical issues that scientists can no longer overlook. The ISSCR guidelines put this research front and centre, making it now impossible for scientists to ignore the important ethical issues that they face. The guidelines also show why ethics must be an integral part of the education of scientists working in these areas.

However, there is a problem with how the guidelines justify that human heritable genome editing should not be permitted at this moment in time. Their main point is that reproductive human heritable genome editing ‘raise[s] unresolved ethical issues’. This is problematic because one could use this same justification for stopping all stem cell research.”

Dr César Palacios-González , Senior Research Fellow in Practical Ethics, Oxford Uehiro Centre for Practical Ethics, University of Oxford

Further Research

Read more about the ethics of chimera, in vitro gametogenesis, and stem cell research:

Chimeras intended for human gamete production: an ethical alternative?   Reproductive Biomedicine Online (2017), 35(4), 387-390. [Palacios-González, César.]

Reproductive genome editing interventions are therapeutic, sometimes . Bioethics (2021). [Palacios‐González, César. ]

The regulation of mitochondrial replacement techniques around the world. Annual Review of Genomics and Human Genetics, 21 (2020): 565-586. [Cohen, I. Glenn, Eli Y. Adashi, Sara Gerke, César Palacios-González, and Vardit Ravitsky]

Human dignity and the creation of human–nonhuman chimeras . Medicine, Health Care and Philosophy, 18, no. 4 (2015): 487-499. [Palacios-González, César]

Multiplex parenting: in vitro gametogenesis and the generations to come . Journal of Medical Ethics, 40, no. 11 (2014): 752-758. [Palacios-González, César, John Harris, and Giuseppe Testa]

Lithuanian National Radio : Radio programme discussing human-monkey embryos , Katrien Devolder (23 April 2021) [Segment begins at 19:50 with an introduction, Dr Devolder's contribution starts at around 21:50]

The Conversation :  First human-monkey embryos created – a small step towards a huge ethical problem , Julian Savulescu and César Palacios-González (22 April 2021)

BBC News :  Human cells grown in monkey embryos spark ethical debate,  Professor Julian Savulescu (by Helen Briggs, 16 April 2021)

The Campus :  Chimeric embryo may have medical implications  (by Gabriella Brady, 23 April 2021) Bionews :  Researchers generate human-monkey chimeric embryos  (by Dr George Janes, 19 April 2021) DT Next : Morality vs Science: Ethics of bridging the human-primate link (by Carla Bleiker, 19 April 2021) Crux Now :  Human-monkey embryo ‘deeply unethical,’ says Catholic bioethicist  (by Charles Collins, 17 April 2021) Conservative Woman :  Today’s talking point  (by Kathy Gyngell, 17 April 2021) Republic World :  Experts Raise Ethical Concerns Over Growing Human Cells In Monkey Embryos , by Riya Baibhawi (17 April 2021) Silicon Republic :  Lab-grown human-monkey embryos raise ethical questions  (by Jenny Darmody, 17 April 2021) Sky News :  Human cells grown in monkey embryos triggers 'Pandora's box' ethical concerns  (16 April 2021) Y108 :  First-ever human-monkey hybrid created in 'chimera' embryo experiment  (by Josh K. Elliott, 16 April 2021) The Sun :  MONKEY ME, MONKEY YOU First part-human, part-monkey embryo created by scientists sparks outcry  (by Charlotte Edwards, 16 April 2021) South China Morning Post:  China-US scientists grow first human-monkey embryo, but is it ethical?  (by Stephen Chen, 16 April 2021) The Guardian :  Human cells grown in monkey embryos reignite ethics debate  (by Nicola Davis, 15 April 2021)

Science :  Lab-grown embryos mix human and monkey cells , Dr Katrien Devolder (by Mitch Leslie, 16 April 2021) Vol. 372, Issue 6539, pp. 223

Quoted in  BioEdge :  Human-monkey chimaeras grown for up to 20 days , (by Michael Cook, 17 April 2021)

The Independent :  What are the ethical implications of growing human cells in monkey embryos?: Ethicists tell The Independent of urgent need for wider debate ahead of more developed experiments , Professor Dominic Wilkinson (by Andy Gregory, 17 April 2021)

BBC Three Counties Radio : Interview on human-monkey chimera experiments, Katrien Devolder (16 April 2021)  [no link]

talkRADIO : Interview on human-monkey chimera experiments , Katrien Devolder (16 April 2021)

BBC World News TV : Interview on human-monkey chimera experiments , Katrien Devolder (16 April 2021)

Times Radio :  Interview on human-monkey chimera experiments , Katrien Devolder (16 April 2021) [no link]

Blogs and Podcasts

Practical Ethics in the News :  Cross-Post: The Moral Status of Human-Monkey Chimeras . Published April 20, 2021 | By Julian Savulescu and Julian Koplin [first published on Pursuit ]

Practical Ethics in the News : Japan to Allow Human-Animal Hybrids to be Brought to Term . Published August 6, 2019 | By Mackenzie Graham

Rethinking Moral Status Workshop : ' Chimeras, Superchimps and Post-persons; Species Boundaries and Moral Status Enhancements ', Sarah Chan (June 2019)

Other recorded sessions of our two-day workshop 'Rethinking Moral Status' are available on our podcast album here .

Cloning and Stem Cell Research (general)

Rethinking moral status, august 2021:.

' Rethinking Moral Status ' (Oxford University Press), edited by Steve Clarke, Hazem Zohny, and Julian Savulescu

• The first volume of its kind to consider how scientific and technological advancements impact our thinking about moral status
• Explores how both current and future developments — from human brain organoids and artificial intelligence, to cyborgs and post-humans — may challenge ideas about moral status
• Presents original ideas and discussion from leading philosophers and bioethicists

Common-sense morality implicitly assumes that reasonably clear distinctions can be drawn between the "full" moral status that is usually attributed to ordinary adult humans, the partial moral status attributed to non-human animals, and the absence of moral status, which is usually ascribed to machines and other artifacts. These implicit assumptions have long been challenged, and are now coming under further scrutiny as there are beings we have recently become able to create, as well as beings that we may soon be able to create, which blur the distinctions between human, non-human animal, and non-biological beings. These beings include non-human chimeras, cyborgs, human brain organoids, post-humans, and human minds that have been uploaded into computers and onto the internet and artificial intelligence. It is far from clear what moral status we should attribute to any of these beings.

There are a number of ways we could respond to the new challenges these technological developments raise: we might revise our ordinary assumptions about what is needed for a being to possess full moral status, or reject the assumption that there is a sharp distinction between full and partial moral status. This volume explores such responses, and provides a forum for philosophical reflection about ordinary presuppositions and intuitions about moral status.

Visit OUP website for further details.  ISBN: 9780192894076

The Ethics of Embryonic Stem Cell Research

Devolder, K., (2015), ' The Ethics of Embryonic Stem Cell Research ', (Oxford: Oxford University Press)

Oxford University Press

Embryonic stem cell research holds unique promise for developing therapies for currently incurable diseases and conditions, and for important biomedical research. However, the process through which embryonic stem cells are obtained involves the destruction of early human embryos. Katrien Devolder focuses on the tension between the popular view that an embryo should never be deliberately harmed or destroyed, and the view that embryonic stem cell research, because of its enormous promise, must go forward. She provides an in-depth ethical analysis of the major philosophical and political attempts to resolve this tension. One such attempt involves the development of a middle ground position, which accepts only types or aspects of embryonic stem cell research deemed compatible with the view that the embryo has a significant moral status. An example is the position that it can be permissible to derive stem cells from embryos left over from in vitro fertilisation but not from embryos created for research. Others have advocated a technical solution. Several techniques have been proposed for deriving embryonic stem cells, or their functional equivalents, without harming embryos. An example is the induced pluripotent stem cell technique. Through highlighting inconsistencies in the arguments for these positions, Devolder argues that the central tension in the embryonic stem cell debate remains unresolved. This conclusion has important implications for the stem cell debate, as well as for policies inspired by this debate.

"As an academic bioethicist with experience in the clinical setting, it is important to me that context and morality are married. Devolder's book accomplishes this task nicely, beginning in the introduction with a consideration of the potential use of embryonic stem cell (if not the embryo as a whole) for the alleviation of pain and disease. She convincingly directs us towards our moral obligation to allieviate suffering, underscoring that embryonic stem cell research is thus a moral enterprise." -  Ayesha Ahmad, London School of Economics,  Times Higher Education

"In her small but well written and insightful monograph Katrien Devolder is focusing on these "middle-ground positions" together with technical solutions to the dilemma. The author has been working on reproductive ethics in general and on embryo and stem cell research ethics in particular for more than ten years. Her book is based on several previously published articles, but it is far more than a mere collection or a re-use of essays." -  Marco Stier,  Ethical Theory and Moral Practice

"Devolders study is a tour de force, exhibiting real skill and imagination in the use of analogies to test our moral intuitions... The Ethics of Embryonic Stem Cell Research  is a solid contribution to our stem cell debates. Neither partisan nor committed to advocacy for any side, it displays epistemic honesty and exhibits the value of philosophical analysis at its best." -  Ronald M. Green,  Monash Bioethics Review

• Wilkinson, D., (2016),  Interview on HFEA decision to approve 'three-person baby’ mitochondrial transfer in UK, Al Jazeera English news channel  (15 December 2016).
• Sandberg, A., (2014). "HowTheLightGetsin:  Planet of the Clones ".  Hosted by Barnaby Martin.  Human cloning is anathema to most of us conjuring up Metropolis visions of identical humans serving tyrannical masters. But might this be a mistaken horror story? Could human cloning instead lead to medical breakthroughs and the end to infertility? The Panel: Dolly the Sheep embryologist Sir Ian Wilmut, outspoken Oxford bioethicist and transhumanist Anders Sandberg and radical sociologist Hilary Rose seek out new life.
• Levy, N., (2013). "Caveman ethics? The rights and wrongs of cloning Neanderthals" The Conversation (26 January).  http://theconversation.com/caveman-ethics-the-rights-and-wrongs-of-cloning-neanderthals-11761
• Savulescu, J. and Powell, R., (2013), 'Mammoth cloning: the ethics'.  The Conversation (reproduced on the  BBC's Religion and Ethics  website) ( 24 July)
• Savulescu, J., (2012), 'Yamanaka Wins Nobel Prize in Ethics'. Der Fritag, German Weekly newspaper. Translated Julian Savulescu opinion piece on Yamanaka’s Nobel Prize (October) Read original blog post  here .
• Savulescu, J., (2011). Interviewed on BBC Radio Foyle re. European Ban on Embryonic Stem Cell Technologies (23 October)
• Savulescu, J. (2008),  Game of Life . Sydney (27 January)
• Savulescu, J. (2008),  Changing the Nature of Human Beings . Sydney
• Savulescu, J. (2007), Interview on cloning for 'The Future' programme (June)
• Savulescu, J. (2007), Catholics Divided over Stem Cells. (14 July)
• Savulescu, J. (2007), Medical Research:  Stem Cell Researchers Risk Excommunication . (8 July)
• Savulescu, J. (2007) Solving the Stem Cell and Cloning Puzzle, The Age
• Savulescu, J. (2006),  Stem Cell Scientists and the Law . (22 August)
• Savulescu, J. (2006),  Australia Human Cloning Vote Saw  "Con Science" Crush Conscience . Dr David Van Gend (11 December)
• Savulescu, J. (2006),  Prominent cardinal attacks science behind stem cells . (11 July)
• Savulescu, J. (2006),  Religous row over stem cell work . (8 July)
• Savulescu, J. (2006),  Stem Cell Scientists Draw up Ethical Charter. Article on Hinxton Group  (25 February)
• Savulescu, J. (2006),  Conflicting laws hinder research.  Report on the formation of the Hinxton Group and the Conference on Transnational Cooperation in Stem Cell Research (25 February)
• Savulescu, J. (2005), Clone Rangers Give the Hard Cell. (20 May)
• Savulescu, J. (2005),  How Will History Judge Cloning , Times Higher Education Supplement, 6 May

Journal Articles

• Pugh, J., (2014), ' Embryos, The Principle of Proportionality, and the Shaky Ground of Moral Respect ', Bioethics, Vol: 28(8): 420–426.
• Pugh, J., (2014), ' Concerns About Eroding the Ethical Barrier to in Vitro Eugenics: Lessons from the hESC Debate ', Journal of Medical Ethics, Vol: 40(11): 737-738. 
• Mathews, D., Donovan, P., Harris, J., Lovell-Badge, R., Savulescu, J. and Faden, R. (2009), 'Pluripotent Stem Cell-Derived Gametes: Truth and (Potential) consequences', Cell Stem Cell, Vol: 5(1) pp. 11-14
• Savulescu, J. (2007),  'The Case for Creating Human-Nonhuman Cell Lines' , Bioethics Forum, Vol: Web based commentary 
• Savulescu, J. and Lott, J. P. (2007), 'A Response to Commentators: "Towards a Global Human Embryonic Stem Cell Bank"', American Journal of Bioethics, Vol: 7 pp. W4- W6
• Savulescu, J. and Lott, J. P. (2007), 'Towards a Global Embryonic Stem Cell Bank', American Journal of Bioethics, Vol: 7 pp. 37
• Savulescu, J., Saunders, R., (2006)  The Hinxton Group Considers Transnational Stem Cell Research , Hastings Centre Report, Volume 36, No.3.
• Savulescu, J., Devolder, K., (2006),  A Defence of Stem Cell and Cloning Research, published as 'The Moral Imperative to Conduct Stem Cell and Cloning Research', in Cambridge Quarterly of Healthcare Ethics 15 (1) pp 7 - 21
• Savulescu, J. (2006),  'Solving the Stem Cell and Cloning Puzzle' , Bioethics Forum, Vol: Web based commentary 
• Savulescu, J. and Devolder, K. (2006), 'The Moral Imperative to Conduct Embryonic Stem Cell and Cloning Research', Cambridge Quarterly of Health Care Ethics, Vol: 15 pp. 7-21
• Savulescu, J., Mathews, D. J. H., Berman, P. R., Donovan, P., Harris, J., Lovell-Badge, R. and Faden, R. (2006), 'Integrity in International Collaboration in Stem Cell Research', Science, Vol: 313
• Levy, N. and Lotz, M. (2005), 'Cloning and a (Kind of) Genetic Fallacy', Bioethics, Vol: 19 pp. 232 - 250
• Liao, S. M. (2005), 'Rescuing Human Embryonic Stem Cell Research: The Blastocyst Transfer Method', American Journal of Bioethics, Vol: 5(6) pp. 8 - 16
• Liao, S. M. (2005), 'Response to Commentators on "Rescuing Human Embryonic Stem Cell Research: The Blastocyte Transfer Method"', American Journal of Bioethics, Vol: 5(6) pp. 10-13 Savulescu, J. and Saunders, R. (2008),  'Research Ethics and Lessons from Hwanggate: what can we learn from the Korean cloning fraud ?' Journal of Medical Ethics, Vol: 34 pp. pp. 214 - 221 
• Savulescu J. (2005)  ‘The ethics of cloning’ . Medicine; 33:2: 18-20
• Savulescu, J. (2005), 'Cloning Benefits Akin to the Discovery of XRays', The Australian, Vol: 4(19)
• Savulescu J. (2004)  Embryo Research: Are There Any Lessons from Natural Reproduction ? Cambridge Health Care Quarterly; 13(1):68-75.
• Savulescu J, Harris J.(2004) ‘ The Creation Lottery: Final Lessons From Natural Reproduction: Why Those Who Accept Natural Reproduction Should Accept Cloning and Other Frankenstein Reproductive Technologies  ’.Cambridge Quarterly of Health Care Ethics;13(1):90-5.
• Savulescu, J., (2002)  The Embryonic Stem Cell Lottery and the Cannibalization of Human Beings , Bioethics 16 pp. 508- 529
• Savulescu, J.,(2000), The ethics of cloning and creating embryonic stem cells as a source of tissue for transplantation: time to change the law in Australia . Australian and New Zealand Journal of Medicine, 30:492-8. 

Minor Publications

• Douglas, T., Harding, C., Bourne, H. and Savulescu, J. (2012). 'Stem Cell Research and Same-Sex Reproduction'. in M. Quigley, S. Chan and J. Harris, (Eds.)   Stem Cells: New Frontiers in Science and Ethics (World Scientific) pp 207-228.
• Savulescu, J. (2007) 'The Case for Creating Human-NonHuman Cell Lines', Bioethics Forum, web based commentary
• Savulescu, J. (2007) 'Humbug Costs Lives' in Parliamentary Brief, October, 1: 7, pp. 27 - 29
• Savulescu, J. (2006), 'Solving the Stem Cell and Cloning Puzzle', Bioethics Forum, Vol: Web based commentary
• Savulescu J.(2005), 'Cloning benefits akin to discovery of X-rays', The Australian 2005 Jun 4:19.
• Savulescu, J. Ethics of Stem Cell Cloning and Research
• Savulescu, J.,Cloning and Embryonic Stem Cell Technologies

The Ethics of Human Cloning and Stem Cell Research

• Markkula Center for Applied Ethics
• Focus Areas
• Bioethics Resources

Report from a conference on state regulation of cloning and stem cell research.

"California Cloning: A Dialogue on State Regulation" was convened October 12, 2001, by the Markkula Center for Applied Ethics at Santa Clara University. Its purpose was to bring together experts from the fields of science, religion, ethics, and law to discuss how the state of California should proceed in regulating human cloning and stem cell research.

A framework for discussing the issue was provided by Center Director of Biotechnology and Health Care Ethics Margaret McLean, who also serves on the California State Advisory Committee on Human Cloning. In 1997, the California legislature declared a "five year moratorium on cloning of an entire human being" and requested that "a panel of representatives from the fields of medicine, religion, biotechnology, genetics, law, bioethics and the general public" be established to evaluate the "medical, ethical and social implications" of human cloning (SB 1344). This 12-member Advisory Committee on Human Cloning convened five public meetings, each focusing on a particular aspect of human cloning: e.g., reproductive cloning, and cloning technology and stem cells. The committee is drafting a report to the legislature that is due on December 31, 2001. The report will discuss the science of cloning, and the ethical and legal considerations of applications of cloning technology. It will also set out recommendations to the legislature regarding regulation of human cloning. The legislature plans to take up this discussion after January. The moratorium expires the end of 2002.

What should the state do at that point? More than 80 invited guests came to SCU for "California Cloning" to engage in a dialogue on that question. These included scientists, theologians, businesspeople from the biotechnology industry, bioethicists, legal scholars, representatives of non-profits, and SCU faculty. Keynote Speaker Ursula Goodenough, professor of biology at Washington University and author of Genetics , set the issues in context with her talk, "A Religious Naturalist Thinks About Bioethics." Four panels addressed the specific scientific, religious, ethical, and legal implications of human reproductive cloning and stem cell research. This document gives a brief summary of the issues as they were raised by the four panels.

Science and Biotechnology Perspectives

Thomas Okarma, CEO of Geron Corp., launched this panel with an overview of regenerative medicine and distinguished between reproductive cloning and human embryonic stem cell research. He helped the audience understand the science behind the medical potential of embryonic stem cell research, with an explanation of the procedures for creating stem cell lines and the relationship of this field to telomere biology and genetics. No brief summary could do justice to the science. The reader is referred to the report of the National Bioethics Advisory Committee (http://bioethics.georgetown.edu/nbac/stemcell.pdf) for a good introduction.

Responding to Okarma, were J. William Langston, president of the Parkinson’s Institute, and Phyllis Gardner, associate professor of medicine and former dean for medical education at Stanford University. Both discussed the implications of the president’s recent restrictions on stem cell research for the non-profit sector. Langston compared the current regulatory environment to the Reagan era ban on fetal cell research, which he believed was a serious setback for Parkinson’s research. He also pointed out that stem cell research was only being proposed using the thousands of embryos that were already being created in the process of fertility treatments. These would ultimately be disposed of in any event, he said, arguing that it would be better to allow them to serve some function rather than be destroyed. President Bush has confined federally-funded research to the 64 existing stem cell lines, far too few in Langston’s view. In addition, Langston opposed bans on government funding for stem cell research because of the opportunities for public review afforded by the process of securing government grants.

Gardner talked about the differences between academic and commercial research, suggesting that both were important for the advancement of science and its application. Since most of the current stem cell lines are in the commercial sector and the president has banned the creation of new lines, she worried that universities would not continue to be centers of research in this important area. That, she argued, would cut out the more serendipitous and sometimes more altruistic approaches of academic research. Also, it might lead to more of the brain drain represented by the recent move of prominent UCSF stem cell researcher Roger Pedersen to Britain. Gardner expressed a hope that the United States would continue to be the "flagship" in stem cell research. Her concerns were echoed later by moderator Allen Hammond, SCU law professor, who urged the state, which has been at the forefront of stem cell research to consider the economic impact of banning such activity. All three panelists commended the decision of the state advisory committee to deal separately with the issues of human cloning and stem cell research.

Religious Perspectives

Two religion panelists, Suzanne Holland and Laurie Zoloth, are co editors of The Human Embryonic Stem Cell Debate: Science, Ethics and Public Policy (MIT Press, 2001). Holland, assistant professor of Religious and Social Ethics at the University of Puget Sound, began the panel with a discussion of Protestant ideas about the sin of pride and respect for persons and how these apply to human reproductive cloning. Given current safety concerns about cloning, she was in favor of a continuing ban. But ultimately, she argued, cloning should be regulated rather than banned outright. In fact, she suggested, the entire fertility industry requires more regulation. As a basis for such regulation, she proposed assessing the motivation of those who want to use the technology. Those whose motives arise from benevolence--for example, those who want to raise a child but have no other means of bearing a genetically related baby--should be allowed to undergo a cloning procedure. Those whose motives arise more from narcissistic considerations -- people who want immortality or novelty -- should be prohibited from using the technology. She proposed mandatory counseling and a waiting period as a means of assessing motivation.

Zoloth reached a different conclusion about reproductive cloning based on her reading of Jewish sources. She argued that the availability of such technology would make human life too easily commodified, putting the emphasis more on achieving a copy of the self than on the crucial parental act of creating "a stranger to whom you would give your life." She put the cloning issue in the context of a system where foster children cannot find homes and where universal health care is not available for babies who have already been born. While Zoloth reported that Jewish ethicists vary considerably in their views about reproductive cloning, there is fairly broad agreement that stem cell research is justified. Among the Jewish traditions she cited were:

The embryo does not have the status of a human person.

There is a commandment to heal.

Great latitude is permitted for learning.

The world is uncompleted and requires human participation to become whole.

Catholic bioethicist Albert Jonsen, one of the deans of the field, gave a historical perspective on the cloning debate, citing a paper by Joshua Lederburg in the 1960s, which challenged his colleagues to look at the implications of the then-remote possibility. He also traced the development of Catholic views on other new medical technologies. When organ transplantation was first introduced, it was opposed as a violation of the principal, "First, do no harm" and as a mutilation of the human body. Later, the issue was reconceived in terms of charity and concern for others. One of the key questions, Jonsen suggested, is What can we, as a society that promotes religious pluralism, do when we must make public policy on issues where religious traditions may disagree. He argued that beneath the particular teachings of each religion are certain broad themes they share, which might provide a framework for the debate. These include human finitude, human fallibility, human dignity, and compassion.

Ethics Perspectives

Lawrence Nelson, adjunct associate professor of philosophy at SCU, opened the ethics panel with a discussion of the moral status of the human embryo. Confining his remarks to viable, extracorporeal embryos (embryos created for fertility treatments that were never implanted), Nelson argued that these beings do have some moral status--albeit it weak--because they are alive and because they are valued to varying degrees by other moral agents. This status does entitle the embryo to some protection. In Nelson’s view, the gamete sources whose egg and sperm created these embryos have a unique connection to them and should have exclusive control over their disposition. If the gamete sources agree, Nelson believes the embryos can be used for research if they are treated respectfully. Some manifestations of respect might be:

They are used only if the goal of the research cannot be obtained by other methods.

The embryos have not reached gastrulation (prior to 14 to 18 days of development).

Those who use them avoid considering or treating them as property.

Their destruction is accompanied by some sense of loss or sorrow.

Philosophy Professor Barbara MacKinnon (University of San Francisco), editor of Human Cloning: Science, Ethics, and Public Policy , began by discussing the distinction between reproductive and therapeutic cloning and the slippery slope argument. She distinguished three different forms of this argument and showed that for each, pursuing stem cell research will not inevitably lead to human reproductive cloning. MacKinnon favored a continuing ban on the latter, citing safety concerns. Regarding therapeutic cloning and stem cell research, she criticized consequentialist views such as that anything can be done to reduce human suffering and that certain embryos would perish anyway. However, she noted that non-consequentialist concerns must also be addressed for therapeutic cloning, among them the question of the moral status of the early embryo. She also made a distinction between morality and the law, arguing that not everything that is immoral ought to be prohibited by law, and showed how this position relates to human cloning.

Paul Billings, co-founder of GeneSage, has been involved in crafting an international treaty to ban human reproductive cloning and germ-line genetic engineering. As arguments against human cloning he cited:

There is no right to have a genetically related child.

Cloning is not safe.

Cloning is not medically necessary.

Cloning could not be delivered in an equitable manner.

Billings also believes that the benefits of stem cell therapies have been "wildly oversold." Currently, he argues, there are no effective treatments coming from this research. He is also concerned about how developing abilities in nuclear transfer technology may have applications in germ-line genetic engineering that we do not want to encourage. As a result, he favors the current go-slow approach of banning the creation of new cell lines until some therapies have been proven effective. At the same time, he believes we must work to better the situation of the poor and marginalized so their access to all therapies is improved.

Legal Perspectives

Member of the State Advisory Committee on Human Cloning Henry "Hank" Greely addressed some of the difficulties in creating a workable regulatory system for human reproductive cloning. First he addressed safety, which, considering the 5 to 10 times greater likelihood of spontaneous abortion in cloned sheep, he argued clearly justifies regulation. The FDA has currently claimed jurisdiction over this technology, but Greely doubted whether the courts would uphold this claim. Given these facts, Greely saw three alternatives for the state of California:

Do nothing; let the federal government take care of it.

Create an FDA equivalent to regulate the safety of the process, an alternative he pointed out for which the state has no experience.

Continue the current ban on the grounds of safety until such time as the procedure is adjudged safe. Next Greely responded to suggestions that the state might regulate by distinguishing between prospective cloners on the basis of their motivation, for example, denying a request to clone a person to provide heart tissue for another person but okaying a request if cloning were the only opportunity a couple might have to conceive a child. Greely found the idea of the state deciding on such basis deeply troubling because it would necessitate "peering into someone’s soul" in a manner that government is not adept at doing.

The impact of regulation on universities was the focus of Debra Zumwalt’s presentation. As Stanford University general counsel, Zumwalt talked about the necessity of creating regulations that are clear and simple. Currently, federal regulations on stem cells are unclear, she argued, making it difficult for universities and other institutions to tell if they are in compliance. She believes that regulations should be based on science and good public policy rather than on politics. As a result, she favored overall policy being set by the legislature but details being worked out at the administrative level by regulatory agencies with expertise. Whatever regulations California develops should not be more restrictive than the federal regulations, she warned, or research would be driven out of the state. Like several other speakers, Zumwalt was concerned about federal regulations restricting stem cell research to existing cell lines. That, she feared, would drive all research into private hands. "We must continue to have a public knowledge base," she said. Also, she praised the inherent safeguards in academic research including peer review, ethics panels, and institutional review boards.

SCU Presidential Professor of Ethics and the Common Good June Carbone looked at the role of California cloning decisions in contributing to the governance of biotechnology. California, she suggested, cannot address these issues alone, and thus might make the most useful contribution by helping to forge a new international moral consensus through public debate. Taking a lesson from U.S. response to recent terrorist attacks, she argued for international consensus based on the alliance of principle and self-interest. Such consensus would need to be enforced both by carrot and stick and should, she said, include a public-private partnership to deal with ethical issues. Applying these ideas to reproductive cloning, she suggested that we think about which alliances would be necessary to prevent or limit the practice. Preventing routine use might be accomplished by establishing a clear ethical and professional line prohibiting reproductive cloning. Preventing exceptional use (a determined person with sufficient money to find a willing doctor) might not be possible. As far as stem cell research is concerned, Carbone argued that the larger the investment in such research, the bigger the carrot--the more the funder would be able to regulate the process. That, she suggested, argues for a government role in the funding. If the professional community does not respect the ethical line drawn by politicians, and alternative funding is available from either public sources abroad or private sources at home, the U.S. political debate runs the risk of becoming irrelevant.

"California Cloning" was organized by the Markkula Center for Applied Ethics and co-sponsored by the Bannan Center for Jesuit Education and Christian Values; the Center for Science, Technology, and Society; the SCU School of Law; the High Tech Law Institute; the Howard Hughes Medical Institute Community of Science Scholars Initiative; and the law firm of Latham & Watkins.

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National Academy of Sciences (US), National Academy of Engineering (US), Institute of Medicine (US) and National Research Council (US) Committee on Science, Engineering, and Public Policy. Scientific and Medical Aspects of Human Reproductive Cloning. Washington (DC): National Academies Press (US); 2002.

Scientific and Medical Aspects of Human Reproductive Cloning.

• Hardcopy Version at National Academies Press

2 Cloning: Definitions And Applications

In this chapter, we address the following questions in our task statement:

What does cloning of animals including humans mean? What are its purposes? How does it differ from stem cell research?

To organize its response to those questions, the panel developed a series of subquestions, which appear as the section headings in the following text.

• WHAT IS MEANT BY REPRODUCTIVE CLONING OF ANIMALS INCLUDING HUMANS?

Reproductive cloning is defined as the deliberate production of genetically identical individuals. Each newly produced individual is a clone of the original. Monozygotic (identical) twins are natural clones. Clones contain identical sets of genetic material in the nucleus—the compartment that contains the chromosomes—of every cell in their bodies. Thus, cells from two clones have the same DNA and the same genes in their nuclei.

All cells, including eggs, also contain some DNA in the energy-generating “factories” called mitochondria. These structures are in the cytoplasm, the region of a cell outside the nucleus. Mitochondria contain their own DNA and reproduce independently. True clones have identical DNA in both the nuclei and mitochondria, although the term clones is also used to refer to individuals that have identical nuclear DNA but different mitochondrial DNA.

• HOW IS REPRODUCTIVE CLONING DONE?

Two methods are used to make live-born mammalian clones. Both require implantation of an embryo in a uterus and then a normal period of gestation and birth. However, reproductive human or animal cloning is not defined by the method used to derive the genetically identical embryos suitable for implantation. Techniques not yet developed or described here would nonetheless constitute cloning if they resulted in genetically identical individuals of which at least one were an embryo destined for implantation and birth.

The two methods used for reproductive cloning thus far are as follows:

• Cloning using somatic cell nuclear transfer ( SCNT ) [ 1 ]. This procedure starts with the removal of the chromosomes from an egg to create an enucleated egg. The chromosomes are replaced with a nucleus taken from a somatic (body) cell of the individual or embryo to be cloned. This cell could be obtained directly from the individual, from cells grown in culture, or from frozen tissue. The egg is then stimulated, and in some cases it starts to divide. If that happens, a series of sequential cell divisions leads to the formation of a blastocyst, or preimplantation embryo. The blastocyst is then transferred to the uterus of an animal. The successful implantation of the blastocyst in a uterus can result in its further development, culminating sometimes in the birth of an animal. This animal will be a clone of the individual that was the donor of the nucleus. Its nuclear DNA has been inherited from only one genetic parent.

The number of times that a given individual can be cloned is limited theoretically only by the number of eggs that can be obtained to accept the somatic cell nuclei and the number of females available to receive developing embryos. If the egg used in this procedure is derived from the same individual that donates the transferred somatic nucleus, the result will be an embryo that receives all its genetic material—nuclear and mitochondrial—from a single individual. That will also be true if the egg comes from the nucleus donor's mother, because mitochondria are inherited maternally. Multiple clones might also be produced by transferring identical nuclei to eggs from a single donor. If the somatic cell nucleus and the egg come from different individuals, they will not be identical to the nuclear donor because the clones will have somewhat different mitochondrial genes [ 2 ; 3 ]

• Cloning by embryo splitting. This procedure begins with in vitro fertilization ( IVF ): the union outside the woman's body of a sperm and an egg to generate a zygote. The zygote (from here onwards also called an embryo) divides into two and then four identical cells. At this stage, the cells can be separated and allowed to develop into separate but identical blastocysts, which can then be implanted in a uterus. The limited developmental potential of the cells means that the procedure cannot be repeated, so embryo splitting can yield only two identical mice and probably no more than four identical humans.

The DNA in embryo splitting is contributed by germ cells from two individuals—the mother who contributed the egg and the father who contributed the sperm. Thus, the embryos, like those formed naturally or by standard IVF , have two parents. Their mitochondrial DNA is identical. Because this method of cloning is identical with the natural formation of monozygotic twins and, in rare cases, even quadruplets, it is not discussed in detail in this report.

• WILL CLONES LOOK AND BEHAVE EXACTLY THE SAME?

Even if clones are genetically identical with one another, they will not be identical in physical or behavioral characteristics, because DNA is not the only determinant of these characteristics. A pair of clones will experience different environments and nutritional inputs while in the uterus, and they would be expected to be subject to different inputs from their parents, society, and life experience as they grow up. If clones derived from identical nuclear donors and identical mitocondrial donors are born at different times, as is the case when an adult is the donor of the somatic cell nucleus, the environmental and nutritional differences would be expected to be more pronounced than for monozygotic (identical) twins. And even monozygotic twins are not fully identical genetically or epigenetically because mutations, stochastic developmental variations, and varied imprinting effects (parent-specific chemical marks on the DNA) make different contributions to each twin [ 3 ; 4 ].

Additional differences may occur in clones that do not have identical mitochondria. Such clones arise if one individual contributes the nucleus and another the egg—or if nuclei from a single individual are transferred to eggs from multiple donors. The differences might be expected to show up in parts of the body that have high demands for energy—such as muscle, heart, eye, and brain—or in body systems that use mitochondrial control over cell death to determine cell numbers [ 5 ; 6 ].

• WHAT ARE THE PURPOSES OF REPRODUCTIVE CLONING?

Cloning of livestock [ 1 ] is a means of replicating an existing favorable combination of traits, such as efficient growth and high milk production, without the genetic “lottery” and mixing that occur in sexual reproduction. It allows an animal with a particular genetic modification, such as the ability to produce a pharmaceutical in milk, to be replicated more rapidly than does natural mating [ 7 ; 8 ]. Moreover, a genetic modification can be made more easily in cultured cells than in an intact animal, and the modified cell nucleus can be transferred to an enucleated egg to make a clone of the required type. Mammals used in scientific experiments, such as mice, are cloned as part of research aimed at increasing our understanding of fundamental biological mechanisms.

In principle, those people who might wish to produce children through human reproductive cloning [ 9 ] include:

• Infertile couples who wish to have a child that is genetically identical with one of them, or with another nucleus donor
• Other individuals who wish to have a child that is genetically identical with them, or with another nucleus donor
• Parents who have lost a child and wish to have another, genetically identical child
• People who need a transplant (for example, of cord blood) to treat their own or their child's disease and who therefore wish to collect genetically identical tissue from a cloned fetus or newborn.

Possible reasons for undertaking human reproductive cloning have been analyzed according to their degree of justification. For example, in reference 10 it is proposed that human reproductive cloning aimed at establishing a genetic link to a gametically infertile parent would be more justifiable than an attempt by a sexually fertile person aimed at choosing a specific genome.

Transplantable tissue may be available without the need for the birth of a child produced by cloning. For example, embryos produced by in vitro fertilization ( IVF ) can be typed for transplant suitability, and in the future stem cells produced by nuclear transplantation may allow the production of transplantable tissue.

The alternatives open to infertile individuals are discussed in Chapter 4 .

• HOW DOES REPRODUCTIVE CLONING DIFFER FROM STEM CELL RESEARCH?

The recent and current work on stem cells that is briefly summarized below and discussed more fully in a recent report from the National Academies entitled Stem Cells and the Future of Regenerative Medicine [ 11 ] is not directly related to human reproductive cloning. However, the use of a common initial step—called either nuclear transplantation or somatic cell nuclear transfer ( SCNT )—has led Congress to consider bills that ban not only human reproductive cloning but also certain areas of stem cell research. Stem cells are cells that have the ability to divide repeatedly and give rise to both specialized cells and more stem cells. Some, such as some blood and brain stem cells, can be derived directly from adults [ 12 - 19 ] and others can be obtained from preimplantation embryos. Stem cells derived from embryos are called embryonic stem cells ( ES cells ). The above-mentioned report from the National Academies provides a detailed account of the current state of stem cell research [ 11 ].

ES cells are also called pluripotent stem cells because their progeny include all cell types that can be found in a postimplantation embryo, a fetus, and a fully developed organism. They are derived from the inner cell mass of early embryos (blastocysts) [ 20 - 23 ]. The cells in the inner cell mass of a given blastocyst are genetically identical, and each blastocyst yields only a single ES cell line. Stem cells are rarer [ 24 ] and more difficult to find in adults than in preimplantation embryos, and it has proved harder to grow some kinds of adult stem cells into cell lines after isolation [ 25 ; 26 ].

Production of different cells and tissues from ES cells or other stem cells is a subject of current research [ 11 ; 27 - 31 ]. Production of whole organs other than bone marrow (to be used in bone marrow transplantation) from such cells has not yet been achieved, and its eventual success is uncertain.

Current interest in stem cells arises from their potential for the therapeutic transplantation of particular healthy cells, tissues, and organs into people suffering from a variety of diseases and debilitating disorders. Research with adult stem cells indicates that they may be useful for such purposes, including for tissues other than those from which the cells were derived [ 12 ; 14 ; 17 ; 18 ; 25 - 27 ; 32 - 43 ]. On the basis of current knowledge, it appears unlikely that adults will prove to be a sufficient source of stem cells for all kinds of tissues [ 11 ; 44 - 47 ]. ES cell lines are of potential interest for transplantation because one cell line can multiply indefinitely and can generate not just one type of specialized cell, but many different types of specialized cells (brain, muscle, and so on) that might be needed for transplants [ 20 ; 28 ; 45 ; 48 ; 49 ]. However, much more research will be needed before the magnitude of the therapeutic potential of either adult stem cells or ES cells will be well understood.

One of the most important questions concerning the therapeutic potential of stem cells is whether the cells, tissues, and perhaps organs derived from them can be transplanted with minimal risk of transplant rejection. Ideally, adult stem cells advantageous for transplantation might be derived from patients themselves. Such cells, or tissues derived from them, would be genetically identical with the patient's own and not be rejected by the immune system. However, as previously described, the availability of sufficient adult stem cells and their potential to give rise to a full range of cell and tissue types are uncertain. Moreover, in the case of a disorder that has a genetic origin, a patient's own adult stem cells would carry the same defect and would have to be grown and genetically modified before they could be used for therapeutic transplantation.

The application of somatic cell nuclear transfer or nuclear transplantation offers an alternative route to obtaining stem cells that could be used for transplantation therapies with a minimal risk of transplant rejection. This procedure—sometimes called therapeutic cloning, research cloning, or nonreproductive cloning, and referred to here as nuclear transplantation to produce stem cells —would be used to generate pluripotent ES cells that are genetically identical with the cells of a transplant recipient [ 50 ]. Thus, like adult stem cells, such ES cells should ameliorate the rejection seen with unmatched transplants.

Two types of adult stem cells—stem cells in the blood forming bone marrow and skin stem cells—are the only two stem cell therapies currently in use. But, as noted in the National Academies' report entitled Stem Cells and the Future of Regenerative Medicine , many questions remain before the potential of other adult stem cells can be accurately assessed [ 11 ]. Few studies on adult stem cells have sufficiently defined the stem cell's potential by starting from a single, isolated cell, or defined the necessary cellular environment for correct differentiation or the factors controlling the efficiency with which the cells repopulate an organ. There is a need to show that the cells derived from introduced adult stem cells are contributing directly to tissue function, and to improve the ability to maintain adult stem cells in culture without the cells differentiating. Finally, most of the studies that have garnered so much attention have used mouse rather than human adult stem cells.

ES cells are not without their own potential problems as a source of cells for transplantation. The growth of human ES cells in culture requires a “feeder” layer of mouse cells that may contain viruses, and when allowed to differentiate the ES cells can form a mixture of cell types at once. Human ES cells can form benign tumors when introduced into mice [ 20 ], although this potential seems to disappear if the cells are allowed to differentiate before introduction into a recipient [ 51 ]. Studies with mouse ES cells have shown promise for treating diabetes [ 30 ], Parkinson's disease [ 52 ], and spinal cord injury [ 53 ].

The ES cells made with nuclear transplantation would have the advantage over adult stem cells of being able to provide virtually all cell types and of being able to be maintained in culture for long periods of time. Current knowledge is, however, uncertain, and research on both adult stem cells and stem cells made with nuclear transplantation is required to understand their therapeutic potentials. (This point is stated clearly in Finding and Recommendation 2 of Stem Cells and the Future of Regenerative Medicine [ 11 ] which states, in part, that “studies of both embryonic and adult human stem cells will be required to most efficiently advance the scientific and therapeutic potential of regenerative medicine.”) It is likely that the ES cells will initially be used to generate single cell types for transplantation, such as nerve cells or muscle cells. In the future, because of their ability to give rise to many cell types, they might be used to generate tissues and, theoretically, complex organs for transplantation. But this will require the perfection of techniques for directing their specialization into each of the component cell types and then the assembly of these cells in the correct proportion and spatial organization for an organ. That might be reasonably straightforward for a simple structure, such as a pancreatic islet that produces insulin, but it is more challenging for tissues as complex as that from lung, kidney, or liver [ 54 ; 55 ].

The experimental procedures required to produce stem cells through nuclear transplantation would consist of the transfer of a somatic cell nucleus from a patient into an enucleated egg, the in vitro culture of the embryo to the blastocyst stage, and the derivation of a pluripotent ES cell line from the inner cell mass of this blastocyst. Such stem cell lines would then be used to derive specialized cells (and, if possible, tissues and organs) in laboratory culture for therapeutic transplantation. Such a procedure, if successful, can avoid a major cause of transplant rejection. However, there are several possible drawbacks to this proposal. Experiments with animal models suggest that the presence of divergent mitochondrial proteins in cells may create “minor” transplantation antigens [ 56 ; 57 ] that can cause rejection [ 58 - 63 ]; this would not be a problem if the egg were donated by the mother of the transplant recipient or the recipient herself. For some autoimmune diseases, transplantation of cells cloned from the patient's own cells may be inappropriate, in that these cells can be targets for the ongoing destructive process. And, as with the use of adult stem cells, in the case of a disorder that has a genetic origin, ES cells derived by nuclear transplantation from the patient's own cells would carry the same defect and would have to be grown and genetically modified before they could be used for therapeutic transplantation. Using another source of stem cells is more likely to be feasible (although immunosuppression would be required) than the challenging task of correcting the one or more genes that are involved in the disease in adult stem cells or in a nuclear transplantation-derived stem cell line initiated with a nucleus from the patient.

In addition to nuclear transplantation, there are two other methods by which researchers might be able to derive ES cells with reduced likeli hood for rejection. A bank of ES cell lines covering many possible genetic makeups is one possibility, although the National Academies report entitled Stem Cells and the Future of Regenerative Medicine rated this as “difficult to conceive” [ 11 ]. Alternatively, embryonic stem cells might be engineered to eliminate or introduce certain cell-surface proteins, thus making the cells invisible to the recipient's immune system. As with the proposed use of many types of adult stem cells in transplantation, neither of these approaches carries anything close to a promise of success at the moment.

The preparation of embryonic stem cells by nuclear transplantation differs from reproductive cloning in that nothing is implanted in a uterus. The issue of whether ES cells alone can give rise to a complete embryo can easily be misinterpreted. The titles of some reports suggest that mouse embryos can be derived from ES cells alone [ 64 - 72 ]. In all cases, however, the ES cells need to be surrounded by cells derived from a host embryo, in particular trophoblast and primitive endoderm. In addition to forming part of the placenta, trophoblast cells of the blastocyst provide essential patterning cues or signals to the embryo that are required to determine the orientation of its future head and rump (anterior-posterior) axis. This positional information is not genetically determined but is acquired by the trophoblast cells from events initiated soon after fertilization or egg activation. Moreover, it is critical that the positional cues be imparted to the inner cells of the blastocyst during a specific time window of development [ 73 - 76 ]. Isolated inner cell masses of mouse blastocysts do not implant by themselves, but will do so if combined with trophoblast vesicles from another embryo [ 77 ]. By contrast, isolated clumps of mouse ES cells introduced into trophoblast vesicles never give rise to anything remotely resembling a postimplantation embryo, as opposed to a disorganized mass of trophoblast. In other words, the only way to get mouse ES cells to participate in normal development is to provide them with host embryonic cells, even if these cells do not remain viable throughout gestation (Richard Gardner, personal communication). It has been reported that human [ 20 ] and primate [ 78 - 79 ] ES cells can give rise to trophoblast cells in culture. However, these trophoblast cells would presumably lack the positional cues normally acquired during the development of a blastocyst from an egg. In the light of the experimental results with mouse ES cells described above, it is very unlikely that clumps of human ES cells placed in a uterus would implant and develop into a fetus. It has been reported that clumps of human ES cells in culture, like clumps of mouse ES cells, give rise to disorganized aggregates known as embryoid bodies [ 80 ].

Besides their uses for therapeutic transplantation, ES cells obtained by nuclear transplantation could be used in laboratories for several types of studies that are important for clinical medicine and for fundamental research in human developmental biology. Such studies could not be carried out with mouse or monkey ES cells and are not likely to be feasible with ES cells prepared from normally fertilized blastocysts. For example, ES cells derived from humans with genetic diseases could be prepared through nuclear transplantation and would permit analysis of the role of the mutated genes in both cell and tissue development and in adult cells difficult to study otherwise, such as nerve cells of the brain. This work has the disadvantage that it would require the use of donor eggs. But for the study of many cell types there may be no alternative to the use of ES cells; for these cell types the derivation of primary cell lines from human tissues is not yet possible.

If the differentiation of ES cells into specialized cell types can be understood and controlled, the use of nuclear transplantation to obtain genetically defined human ES cell lines would allow the generation of genetically diverse cell lines that are not readily obtainable from embryos that have been frozen or that are in excess of clinical need in IVF clinics. The latter do not reflect the diversity of the general population and are skewed toward genomes from couples in which the female is older than the period of maximal fertility or one partner is infertile. In addition, it might be important to produce stem cells by nuclear transplantation from individuals who have diseases associated with both simple [81] and complex (multiple-gene) heritable genetic predilections. For example, some people have mutations that predispose them to “Lou Gehrig's disease” (amyotrophic lateral sclerosis, or ALS); however, only some of these individuals become ill, presumably because of the influence of additional genes. Many common genetic predilections to diseases have similarly complex etiologies; it is likely that more such diseases will become apparent as the information generated by the Human Genome Project is applied. It would be possible, by using ES cells prepared with nuclear transplantation from patients and healthy people, to compare the development of such cells and to study the fundamental processes that modulate predilections to diseases.

Neither the work with ES cells , nor the work leading to the formation of cells and tissues for transplantation, involves the placement of blastocysts in a uterus. Thus, there is no embryonic development beyond the 64 to 200 cell stage, and no fetal development.

2-1. Reproductive cloning involves the creation of individuals that contain identical sets of nuclear genetic material ( DNA ). To have complete genetic identity, clones must have not only the same nuclear genes, but also the same mitochondrial genes.

2-2. Cloned mammalian animals can be made by replacing the chromosomes of an egg cell with a nucleus from the individual to be cloned, followed by stimulation of cell division and implantation of the resulting embryo.

2-3. Cloned individuals, whether born at the same or different times, will not be physically or behaviorally identical with each other at comparable ages.

2-4. Stem cells are cells that have an extensive ability to self-renew and differentiate, and they are therefore important as a potential source of cells for therapeutic transplantation. Embryonic stem cells derived through nuclear transplantation into eggs are a potential source of pluripotent (embryonic) stem cell lines that are immunologically similar to a patient's cells. Research with such cells has the goal of producing cells and tissues for therapeutic transplantation with minimal chance of rejection.

2-5. Embryonic stem cells and cell lines derived through nuclear transplantation could be valuable for uses other than organ transplantation. Such cell lines could be used to study the heritable genetic components associated with predilections to a variety of complex genetic diseases and test therapies for such diseases when they affect cells that are hard to study in isolation in adults.

2-6. The process of obtaining embryonic stem cells through nuclear transplantation does not involve the placement of an embryo in a uterus, and it cannot produce a new individual.

• Cite this Page National Academy of Sciences (US), National Academy of Engineering (US), Institute of Medicine (US) and National Research Council (US) Committee on Science, Engineering, and Public Policy. Scientific and Medical Aspects of Human Reproductive Cloning. Washington (DC): National Academies Press (US); 2002. 2, Cloning: Definitions And Applications.
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Cloning Fact Sheet

The term cloning describes a number of different processes that can be used to produce genetically identical copies of a biological entity. The copied material, which has the same genetic makeup as the original, is referred to as a clone. Researchers have cloned a wide range of biological materials, including genes, cells, tissues and even entire organisms, such as a sheep.

Do clones ever occur naturally?

Yes. In nature, some plants and single-celled organisms, such as bacteria , produce genetically identical offspring through a process called asexual reproduction. In asexual reproduction, a new individual is generated from a copy of a single cell from the parent organism.

Natural clones, also known as identical twins, occur in humans and other mammals. These twins are produced when a fertilized egg splits, creating two or more embryos that carry almost identical DNA . Identical twins have nearly the same genetic makeup as each other, but they are genetically different from either parent.

What are the types of artificial cloning?

There are three different types of artificial cloning: gene cloning, reproductive cloning and therapeutic cloning.

Gene cloning produces copies of genes or segments of DNA. Reproductive cloning produces copies of whole animals. Therapeutic cloning produces embryonic stem cells for experiments aimed at creating tissues to replace injured or diseased tissues.

Gene cloning, also known as DNA cloning, is a very different process from reproductive and therapeutic cloning. Reproductive and therapeutic cloning share many of the same techniques, but are done for different purposes.

What sort of cloning research is going on at NHGRI?

Gene cloning is the most common type of cloning done by researchers at NHGRI. NHGRI researchers have not cloned any mammals and NHGRI does not clone humans.

How are genes cloned?

Researchers routinely use cloning techniques to make copies of genes that they wish to study. The procedure consists of inserting a gene from one organism, often referred to as "foreign DNA," into the genetic material of a carrier called a vector. Examples of vectors include bacteria, yeast cells, viruses or plasmids, which are small DNA circles carried by bacteria. After the gene is inserted, the vector is placed in laboratory conditions that prompt it to multiply, resulting in the gene being copied many times over.

How are animals cloned?

In reproductive cloning, researchers remove a mature somatic cell , such as a skin cell, from an animal that they wish to copy. They then transfer the DNA of the donor animal's somatic cell into an egg cell, or oocyte, that has had its own DNA-containing nucleus removed.

Researchers can add the DNA from the somatic cell to the empty egg in two different ways. In the first method, they remove the DNA-containing nucleus of the somatic cell with a needle and inject it into the empty egg. In the second approach, they use an electrical current to fuse the entire somatic cell with the empty egg.

In both processes, the egg is allowed to develop into an early-stage embryo in the test-tube and then is implanted into the womb of an adult female animal.

Ultimately, the adult female gives birth to an animal that has the same genetic make up as the animal that donated the somatic cell. This young animal is referred to as a clone. Reproductive cloning may require the use of a surrogate mother to allow development of the cloned embryo, as was the case for the most famous cloned organism, Dolly the sheep.

What animals have been cloned?

Over the last 50 years, scientists have conducted cloning experiments in a wide range of animals using a variety of techniques. In 1979, researchers produced the first genetically identical mice by splitting mouse embryos in the test tube and then implanting the resulting embryos into the wombs of adult female mice. Shortly after that, researchers produced the first genetically identical cows, sheep and chickens by transferring the nucleus of a cell taken from an early embryo into an egg that had been emptied of its nucleus.

It was not until 1996, however, that researchers succeeded in cloning the first mammal from a mature (somatic) cell taken from an adult animal. After 276 attempts, Scottish researchers finally produced Dolly, the lamb from the udder cell of a 6-year-old sheep. Two years later, researchers in Japan cloned eight calves from a single cow, but only four survived.

Besides cattle and sheep, other mammals that have been cloned from somatic cells include: cat, deer, dog, horse, mule, ox, rabbit and rat. In addition, a rhesus monkey has been cloned by embryo splitting.

Have humans been cloned?

Despite several highly publicized claims, human cloning still appears to be fiction. There currently is no solid scientific evidence that anyone has cloned human embryos.

In 1998, scientists in South Korea claimed to have successfully cloned a human embryo, but said the experiment was interrupted very early when the clone was just a group of four cells. In 2002, Clonaid, part of a religious group that believes humans were created by extraterrestrials, held a news conference to announce the birth of what it claimed to be the first cloned human, a girl named Eve. However, despite repeated requests by the research community and the news media, Clonaid never provided any evidence to confirm the existence of this clone or the other 12 human clones it purportedly created.

In 2004, a group led by Woo-Suk Hwang of Seoul National University in South Korea published a paper in the journal Science in which it claimed to have created a cloned human embryo in a test tube. However, an independent scientific committee later found no proof to support the claim and, in January 2006, Science announced that Hwang's paper had been retracted.

From a technical perspective, cloning humans and other primates is more difficult than in other mammals. One reason is that two proteins essential to cell division, known as spindle proteins, are located very close to the chromosomes in primate eggs. Consequently, removal of the egg's nucleus to make room for the donor nucleus also removes the spindle proteins, interfering with cell division. In other mammals, such as cats, rabbits and mice, the two spindle proteins are spread throughout the egg. So, removal of the egg's nucleus does not result in loss of spindle proteins. In addition, some dyes and the ultraviolet light used to remove the egg's nucleus can damage the primate cell and prevent it from growing.

Do cloned animals always look identical?

No. Clones do not always look identical. Although clones share the same genetic material, the environment also plays a big role in how an organism turns out.

For example, the first cat to be cloned, named Cc, is a female calico cat that looks very different from her mother. The explanation for the difference is that the color and pattern of the coats of cats cannot be attributed exclusively to genes. A biological phenomenon involving inactivation of the X chromosome (See sex chromosome ) in every cell of the female cat (which has two X chromosomes) determines which coat color genes are switched off and which are switched on. The distribution of X inactivation, which seems to occur randomly, determines the appearance of the cat's coat.

What are the potential applications of cloned animals?

Reproductive cloning may enable researchers to make copies of animals with the potential benefits for the fields of medicine and agriculture.

For instance, the same Scottish researchers who cloned Dolly have cloned other sheep that have been genetically modified to produce milk that contains a human protein essential for blood clotting. The hope is that someday this protein can be purified from the milk and given to humans whose blood does not clot properly. Another possible use of cloned animals is for testing new drugs and treatment strategies. The great advantage of using cloned animals for drug testing is that they are all genetically identical, which means their responses to the drugs should be uniform rather than variable as seen in animals with different genetic make-ups.

After consulting with many independent scientists and experts in cloning, the U.S. Food and Drug Administration (FDA) decided in January 2008 that meat and milk from cloned animals, such as cattle, pigs and goats, are as safe as those from non-cloned animals. The FDA action means that researchers are now free to using cloning methods to make copies of animals with desirable agricultural traits, such as high milk production or lean meat. However, because cloning is still very expensive, it will likely take many years until food products from cloned animals actually appear in supermarkets.

Another application is to create clones to build populations of endangered, or possibly even extinct, species of animals. In 2001, researchers produced the first clone of an endangered species: a type of Asian ox known as a guar. Sadly, the baby guar, which had developed inside a surrogate cow mother, died just a few days after its birth. In 2003, another endangered type of ox, called the Banteg, was successfully cloned. Soon after, three African wildcats were cloned using frozen embryos as a source of DNA. Although some experts think cloning can save many species that would otherwise disappear, others argue that cloning produces a population of genetically identical individuals that lack the genetic variability necessary for species survival.

Some people also have expressed interest in having their deceased pets cloned in the hope of getting a similar animal to replace the dead one. But as shown by Cc the cloned cat, a clone may not turn out exactly like the original pet whose DNA was used to make the clone.

What are the potential drawbacks of cloning animals?

Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of 277 cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning.

Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart. Other consequences include premature aging and problems with the immune system. Another potential problem centers on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink. Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types. As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age. Dolly died when she was six years old, about half the average sheep's 12-year lifespan.

What is therapeutic cloning?

Therapeutic cloning involves creating a cloned embryo for the sole purpose of producing embryonic stem cells with the same DNA as the donor cell. These stem cells can be used in experiments aimed at understanding disease and developing new treatments for disease. To date, there is no evidence that human embryos have been produced for therapeutic cloning.

The richest source of embryonic stem cells is tissue formed during the first five days after the egg has started to divide. At this stage of development, called the blastocyst, the embryo consists of a cluster of about 100 cells that can become any cell type. Stem cells are harvested from cloned embryos at this stage of development, resulting in destruction of the embryo while it is still in the test tube.

What are the potential applications of therapeutic cloning?

Researchers hope to use embryonic stem cells, which have the unique ability to generate virtually all types of cells in an organism, to grow healthy tissues in the laboratory that can be used replace injured or diseased tissues. In addition, it may be possible to learn more about the molecular causes of disease by studying embryonic stem cell lines from cloned embryos derived from the cells of animals or humans with different diseases. Finally, differentiated tissues derived from ES cells are excellent tools to test new therapeutic drugs.

What are the potential drawbacks of therapeutic cloning?

Many researchers think it is worthwhile to explore the use of embryonic stem cells as a path for treating human diseases. However, some experts are concerned about the striking similarities between stem cells and cancer cells. Both cell types have the ability to proliferate indefinitely and some studies show that after 60 cycles of cell division, stem cells can accumulate mutations that could lead to cancer. Therefore, the relationship between stem cells and cancer cells needs to be more clearly understood if stem cells are to be used to treat human disease.

What are some of the ethical issues related to cloning?

Gene cloning is a carefully regulated technique that is largely accepted today and used routinely in many labs worldwide. However, both reproductive and therapeutic cloning raise important ethical issues, especially as related to the potential use of these techniques in humans.

Reproductive cloning would present the potential of creating a human that is genetically identical to another person who has previously existed or who still exists. This may conflict with long-standing religious and societal values about human dignity, possibly infringing upon principles of individual freedom, identity and autonomy. However, some argue that reproductive cloning could help sterile couples fulfill their dream of parenthood. Others see human cloning as a way to avoid passing on a deleterious gene that runs in the family without having to undergo embryo screening or embryo selection.

Therapeutic cloning, while offering the potential for treating humans suffering from disease or injury, would require the destruction of human embryos in the test tube. Consequently, opponents argue that using this technique to collect embryonic stem cells is wrong, regardless of whether such cells are used to benefit sick or injured people.

Last updated: August 15, 2020

Religious beliefs shape our thinking on cloning, stem cells and gene editing

Christianity, Judaism, Hinduism, Buddhism and Islam react to new technologies and concepts in their own way – though there is rarely universal consensus on every issue within those religions. Not surprisingly, the basis for modern day beliefs is often found in scripture and related lore.

To better understand, for example,  how religions view the use of human embryonic tissue for research and treatment, consider the ancient Jewish tales of golemim — super beings created by humans for protection and tasks.

Whereas Christian tradition for many centuries had a prohibition against this kind of “playing God,” Judaism offers many tales of people doing just that. Stories and parables about people creating synthetic life are mentioned in Jewish texts — notably the Talmud and the Zohar. These texts took form from late antiquity through the Middle Ages and into early modern times. They offer insights into how modern Jewish perspectives on biotechnology differ substantially from those of Christianity, whose scholars tend to put more weight on biblical passages.

One interesting tale from the Babylonian Talmud (tractate Sanhedrin 65b) involves two rabbis who got together just before the Sabbath to use their powers to create from nothing a 3-year-old calf, which they then sacrificed to make a Sabbath veal dinner. Another Talmudic passage ( Sanhedrin 38b) describes the mythical Adam of biblical Genesis being created first as a golem. Later he is enhanced with consciousness.

Use of the word enhanced is intentional here. It’s not to imply that any Medieval Jewish commentary has any scientific relevance v is-a-vis transhumanism, or other applications of biotechnology, but because modern Jewish scholars see them as a kind of foreshadowing of current times in terms of ethical implications and potential dilemmas.

One interesting element of the golem tales is that they often go out of control and wreak havoc. This underlies a perspective in Jewish thinking that one should be cautious in applying biotechnology. But it also may suggest there is nothing prohibiting one from engaging in research and development in the first place — whether we’re talking about GM crops, cloning, chimeric organs, or genome editing, so long as policy makers and regulators take care to assure that the technology is put to beneficial use with appropriate safeguards.

While Islam doesn’t have a formalized collection of commentaries akin to the Talmud, practically speaking, Muslim perspective closely mirrors Jewish perspective. Hinduism takes a similar approach in that there are no particular principles that could be seen as a basis for prohibiting biotech development.

Christianity is a different story. The concept of “playing God” still bothers certain groups. Christian opinion on GMOs is split. However, when it comes to therapeutic cloning via  somatic cell nuclear transfer (SCNT) to create embryonic stem cells , or use of embryos that have been created by in vitro fertilization (IVF) in fertility clinics, Christian views tend to be more prohibitive compared with other religions.

This is not to say there’s no crossover in opinion between Christians and non-Christians. An old saying goes that if you have two Jews, you have three opinions (and the same probably applies to Hindus, Muslims, Buddhists and Christians too). This became apparent as a fascinating discussion played out at Harvard University when representatives from Islam, Judaism and two sects of Protestant Christianity got together to discuss human embryonic stem cell research in 2007.

Assigned to present the Jewish view on embryology relevant to stem cell research, Eric Cohen, director of the Bioethics and American Democracy program at the Ethics and Public Policy Center in Washington, D.C., started out doing just that. But over the course of the discussion, it became apparent that his own personal view aligned closer to that of a Christian — he assigned high moral value to human embryos and failed to distinguish an embryo from a blastocyst, a very early developmental stage that is really where human embryonic stem cell research is focused. In contrast to Cohen, Professor Omar Sultan Haque, of Harvard Medical School, sounded like he was in line with the mainstream Jewish view, even though he was presenting the Islamic perspective. But as we’ll see a little later, the Jewish and Muslim perspectives on life prior to birth — as well as an emphasis on doing good for the public and health — are very similar.

Comparison of religious perspectives on GM food

Hinduism and Islam generally have no inherent problem with GM crops.

“Apart [from] a few key factors, concepts like karma and rebirth, most of the people we call Hindu would probably not agree on many of the issues,” said Hindu scholar Vasudha Narayanan in an interview with VICE News. The basic approach to technology in Hinduism is to accept it based on its practical value, but when it comes to specific religious rituals, that’s when Hindus may take issue. “They may have it in the regular food, but they may not do it in offerings of food to the deity in a temple,” Narayanan added. “There would be ritual contexts in which GMOs might not be used.”

The question of Islamic feelings on the subject was addressed in the same Vice article by Ebrahim Moosa, a University of Notre Dame Islamic Studies professor: “I have seen people who have adopted a position of caution and said one has to watch this issue. It’s not a question of permissible or impermissible, but what is good for our society.”

Mainline Protestant sects of Christianity tend to have no particular objection to GM crops, though the Roman Catholic Church has some concerns according to a 2015 letter from Pope Francis.  Excerpts only are quoted here for the sake of brevity. In recent years, smaller bits of it have been cherry-picked by anti-GMO activist groups to support claims that the Pope “ slammed GMOs “, but it really presents a Vatican that is struggling to understand both the science and the broader issues:

It is difficult to make a general judgement about genetic modification (GM)…Genetic mutations, in fact, have often been, and continue to be, caused by nature itself..In many places, following the introduction of these crops, productive land is concentrated in the hands of a few owners due to “the progressive disappearance of small producers, who, as a consequence of the loss of the exploited lands, are obliged to withdraw from direct production”. The most vulnerable of these become temporary labourers, and many rural workers end up moving to poverty-stricken urban areas…Certainly, these issues require constant attention and a concern for their ethical implications. A broad, responsible scientific and social debate needs to take place, one capable of considering all the available information and of calling things by their name….This is a complex environmental issue; it calls for a comprehensive approach which would require, at the very least, greater efforts to finance various lines of independent, interdisciplinary research capable of shedding new light on the problem.

Judaism has no problem with scientists fiddling around with plant genetics. It’s possible to find naysayer rabbis here and there who buy into the same activist concerns that seem to have influenced the Pope, but the general perspective from Judaism is that crops that improve human health and the food supply are beneficial, regardless of how they are made. Thus, when you ask Jewish scholars about GM food, they usually just want to make sure that you’re not talking about transferring genes from a pig, shellfish, or other non-kosher animal into a plant. Thus far, no such transgenic pig plant has come onto the market, and so for religious Jews, GMOs are not likely to become a major concern.

On the contrary, when considering GMOs developed for humanitarian goals — Golden Rice, for example — precedent upon precedent in Jewish law and scholarship weighs heavily in favor of the technology. This has to do with the Jewish concept of tikkun olam — repairing the world.

Conflicting views on when an embryo becomes a person

Embryo-based therapies include use of embryonic stem cells to grow new tissue to replace degenerated tissue, such as in neurodegenerative diseases. Embryos can come from donating parents, or they can be created by cloning the patient who is to receive the new tissue. The latter is called therapeutic cloning and it must be distinguished from reproductive cloning in which one creates a baby with her own genetic make up.

Therapeutic cloning has the potential to treat a range of conditions, from type 1 diabetes, to degenerative conditions like Parkinson disease and various blood disorders. There are disagreements within the various religions over the use of this technology. But the major objection to anything involving human tissue comes from Christianity — because of the belief that life begins at conception. The position was expressed in the 2015 letter of Pope Franci s but also reflects views of various Eastern Orthodox and Protestant denominations.

Concern for the protection of nature is also incompatible with the justification of abortion. How can we genuinely teach the importance of concern for other vulnerable beings, however troublesome or inconvenient they may be, if we fail to protect a human embryo? There is a tendency to justify transgressing all boundaries when experimentation is carried out on living human embryos.

Certainly there are some liberal Protestant denominations that disagree. And there are those who believe other considerations — finding cures for horrible diseases, for example — come into play.

Hinduism is not fond of abortion, but India permits termination of pregnancy up to 20 weeks of gestation based on a rationale of freedom of choice similar to that underlying the approach in the United States (characterized by complete freedom of choice for the mother during the first two thirds of pregnancy, but increasing restrictions during weeks when the fetus is viable).

Both Judaism and Islam see human ontogeny (development from gametes through personhood) as a kind of graded progression. The Babylonian Talmud considers the early products of conception (what science now calls the zygote, morula, blastocyst, and early embryonic stages) k’mayim , meaning like water until 40 days into pregnancy (tractate Yevamot 69b). At 40 days gestation, many embryos demonstrate the beginnings of brainwave activity (although obviously Talmudic period rabbis didn’t know this). At this point, there also has been a heartbeat for about 3 weeks seen easily on ultrasound — a fact that anti-abortion Christians use frequently in efforts to dissuade potential mothers from ending their pregnancies. But, being like water, a conceptus has no legal or moral status in Talmudic thinking.

From 40 days through the rest of pregnancy, the embryo/fetus has a status as a kind of property in Jewish law. Thus, somebody who harms a pregnant woman in a way that triggers a spontaneous abortion can be charged for damages. But it is not considered murder, nor even killing, until the next stage, which begins when the fetal head crowns through the vaginal opening. And by the way, that’s not the final stage. In terms of religious ritual surrounding mourning, Judaism does not even see a newborn as completely alive until 31 days after birth. This illustrates a view that personhood develops gradually, and in stages, with development occurring both in utero and after birth. Similarly, in Islam there is a threshold during pregnancy, which the majority of people who think about this say is 120 days (roughly 17 weeks gestation), after which a fetus is considered enough like a person such that a physician who follows Islam would not want to terminate a pregnancy. Even beyond the threshold, however, for many Muslims (as with many Christians at any point in pregnancy), the need to save a mother’s life can supersede fetal needs.

The mothers’ life notwithstanding, the graded views of ontogeny put Jewish and Islamic thinking in line with US laws drafted to conform with the watershed 1973 Supreme Court case Roe versus Wade, establishing fetal viability. Legally, that’s 26 weeks gestation, but medically it has been pushed back somewhere around 23 weeks gestation in a minority of fetuses, but this could change (especially with a new technology called the artificial placenta now on deck to enter clinical trials). The way neonatology is going, along with genetic engineering and other technologies, within decades an artificial womb (to which the artificial placenta is a stepping stone) could become reality. This could turn the tables on abortion policy by altering the paradigm of pro-life versus pro-choice, since a woman’s choice to terminate pregnancy could be satisfied without actually killing the embryo or fetus. Rather, it could simply be transferred into an external life-support environment and developed to term.

Buddhism is the perhaps hardest to categorize when it comes to cloning and related biotechnology. Technically, Buddhism considers a blastocyst a human life, but it also considers the well-being of non-human animals equal to that of humans. Buddhists tend to vary in their opinions on abortion unrelated to their religion, and many are fervently pro-choice. Overall, Buddhism is accepting of human embryonic stem cell research. Northwestern University Medical ethics and religious studies professor, Laurie Zoloth, points out that cloning could even support Buddhist beliefs:

“Buddhism can take account the pluripotential nature of the cells, their genomic and genetic possibilities, and understands a kind of reincarnation,” she said in commentaries appearing in ABC Science Online in 2004 . “To me it’s a good example of the possibility for even deeply held religious beliefs to achieve change from their own resources, texts, and traditions.”

Professor Yong Moon of Seoul National University in South Korea, said almost the same thing, even more bluntly: “Cloning is a different way of thinking about the recycling of life. It’s a Buddhist way of thinking.”

Artificial wombs, viability thresholds, and reincarnation of cell notwithstanding, therapeutic cloning and human embryonic stem cell research really involves just the blastocyst stage of development. At this stage, for all intents and purposes, Judaism, Islam, Hinduism, and essentially all major religions are in agreement and in direct opposition to Christianity. Effectively, this makes the starting point for non-Christian religions essentially the same as the starting point for discussions on human embryonic stem cells in the secular world. So, there really are just two paradigms defining the territory for opinions on embryonic stem cells and things related.

A version of this article originally appeared on the GLP on January 9, 2017.

David Warmflash is an astrobiologist, physician and science writer. BIO . Follow him on Twitter @CosmicEvolution

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ENCYCLOPEDIC ENTRY

Cloning is a technique scientists use to create exact genetic replicas of genes, cells, or animals.

Biology, Genetics, Health, Chemistry

Cloned Beagles

Two Beagle puppies successfully cloned in Seoul, South Korea. These two dogs were cloned by a biopharmaceutical company that specializes in stem cell based therapeutics.

Photograph by Handout

Cloning is a technique scientists use to make exact genetic copies of living things. Genes , cells, tissues, and even whole animals can all be cloned .

Some clones already exist in nature. Single-celled organisms like bacteria make exact copies of themselves each time they reproduce. In humans, identical twins are similar to clones . They share almost the exact same genes . Identical twins are created when a fertilized egg splits in two.

Scientists also make clones in the lab. They often clone genes in order to study and better understand them. To clone a gene , researchers take DNA from a living creature and insert it into a carrier like bacteria or yeast. Every time that carrier reproduces, a new copy of the gene is made.

Animals are cloned in one of two ways. The first is called embryo twinning. Scientists first split an embryo in half. Those two halves are then placed in a mother’s uterus. Each part of the embryo develops into a unique animal, and the two animals share the same genes . The second method is called somatic cell nuclear transfer. Somatic cells are all the cells that make up an organism, but that are not sperm or egg cells. Sperm and egg cells contain only one set of chromosomes , and when they join during fertilization, the mother’s chromosomes merge with the father’s. Somatic cells , on the other hand, already contain two full sets of chromosomes . To make a clone , scientists transfer the DNA from an animal’s somatic cell into an egg cell that has had its nucleus and DNA removed. The egg develops into an embryo that contains the same genes as the cell donor. Then the embryo is implanted into an adult female’s uterus to grow.

In 1996, Scottish scientists cloned the first animal, a sheep they named Dolly. She was cloned using an udder cell taken from an adult sheep. Since then, scientists have cloned cows, cats, deer, horses, and rabbits. They still have not cloned a human, though. In part, this is because it is difficult to produce a viable clone . In each attempt, there can be genetic mistakes that prevent the clone from surviving. It took scientists 276 attempts to get Dolly right. There are also ethical concerns about cloning a human being.

Researchers can use clones in many ways. An embryo made by cloning can be turned into a stem cell factory. Stem cells are an early form of cells that can grow into many different types of cells and tissues. Scientists can turn them into nerve cells to fix a damaged spinal cord or insulin-making cells to treat diabetes.

The cloning of animals has been used in a number of different applications. Animals have been cloned to have gene mutations that help scientists study diseases that develop in the animals. Livestock like cows and pigs have been cloned to produce more milk or meat. Clones can even “resurrect” a beloved pet that has died. In 2001, a cat named CC was the first pet to be created through cloning. Cloning might one day bring back extinct species like the woolly mammoth or giant panda.

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Early cloning experiments

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What is cloning?

Why is cloning controversial.

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• National Geographic - Cloning
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Cloning is the process of generating a genetically identical copy of a cell or an organism. Cloning happens all the time in nature. In biomedical research, cloning is broadly defined to mean the duplication of any kind of biological material for scientific study, such as a piece of  DNA  or an individual cell.

Why is cloning important?

Therapeutic cloning enables the cultivation of stem cells that are genetically identical to a patient. This approach, by avoiding risk of rejection by the immune system, has the potential to benefit many patients, including those affected by Alzheimer disease, diabetes, and spinal cord injury.

The cloning of humans remains universally condemned, primarily for the associated psychological, social, and physiological risks. There are also concerns that cloning promotes  eugenics , the idea that humanity could be improved through the selection of individuals possessing desired traits. There also exists controversy over the ethics of therapeutic and research cloning, which makes use of embryos that are otherwise discarded. 

cloning , the process of generating a genetically identical copy of a cell or an organism. Cloning happens often in nature—for example, when a cell replicates itself asexually without any genetic alteration or recombination . Prokaryotic organisms (organisms lacking a cell nucleus ) such as bacteria create genetically identical duplicates of themselves using binary fission or budding . In eukaryotic organisms (organisms possessing a cell nucleus) such as humans, all the cells that undergo mitosis , such as skin cells and cells lining the gastrointestinal tract , are clones ; the only exceptions are gametes ( eggs and sperm ), which undergo meiosis and genetic recombination.

In biomedical research, cloning is broadly defined to mean the duplication of any kind of biological material for scientific study, such as a piece of DNA or an individual cell. For example, segments of DNA are replicated exponentially by a process known as polymerase chain reaction , or PCR, a technique that is used widely in basic biological research. The type of cloning that is the focus of much ethical controversy involves the generation of cloned embryos , particularly those of humans, which are genetically identical to the organisms from which they are derived, and the subsequent use of these embryos for research, therapeutic, or reproductive purposes.

Reproductive cloning was originally carried out by artificial “twinning,” or embryo splitting, which was first performed on a salamander embryo in the early 1900s by German embryologist Hans Spemann . Later, Spemann, who was awarded the Nobel Prize for Physiology or Medicine (1935) for his research on embryonic development, theorized about another cloning procedure known as nuclear transfer . This procedure was performed in 1952 by American scientists Robert W. Briggs and Thomas J. King, who used DNA from embryonic cells of the frog Rana pipiens to generate cloned tadpoles . In 1958 British biologist John Bertrand Gurdon successfully carried out nuclear transfer using DNA from adult intestinal cells of African clawed frogs ( Xenopus laevis ). Gurdon was awarded a share of the 2012 Nobel Prize in Physiology or Medicine for this breakthrough.

Advancements in the field of molecular biology led to the development of techniques that allowed scientists to manipulate cells and to detect chemical markers that signal changes within cells. With the advent of recombinant DNA technology in the 1970s, it became possible for scientists to create transgenic clones—clones with genomes containing pieces of DNA from other organisms. Beginning in the 1980s mammals such as sheep were cloned from early and partially differentiated embryonic cells. In 1996 British developmental biologist Ian Wilmut generated a cloned sheep, named Dolly , by means of nuclear transfer involving an enucleated embryo and a differentiated cell nucleus. This technique, which was later refined and became known as somatic cell nuclear transfer (SCNT), represented an extraordinary advance in the science of cloning, because it resulted in the creation of a genetically identical clone of an already grown sheep. It also indicated that it was possible for the DNA in differentiated somatic (body) cells to revert to an undifferentiated embryonic stage, thereby reestablishing pluripotency —the potential of an embryonic cell to grow into any one of the numerous different types of mature body cells that make up a complete organism. The realization that the DNA of somatic cells could be reprogrammed to a pluripotent state significantly impacted research into therapeutic cloning and the development of stem cell therapies.

Soon after the generation of Dolly, a number of other animals were cloned by SCNT, including pigs , goats , rats , mice , dogs , horses , and mules . Despite those successes, the birth of a viable SCNT primate clone would not come to fruition until 2018, and scientists used other cloning processes in the meantime. In 2001 a team of scientists cloned a rhesus monkey through a process called embryonic cell nuclear transfer , which is similar to SCNT except that it uses DNA from an undifferentiated embryo. In 2007 macaque monkey embryos were cloned by SCNT, but those clones lived only to the blastocyst stage of embryonic development. It was more than 10 years later, after improvements to SCNT had been made, that scientists announced the live birth of two clones of the crab-eating macaque ( Macaca fascicularis ), the first primate clones using the SCNT process. (SCNT has been carried out with very limited success in humans, in part because of problems with human egg cells resulting from the mother’s age and environmental factors.)

Cloning and Stem Cell Technology

When we follow the pace of scientific progress and technological development and modern science and how it is faster than we imagine and what we expected, we think how life was twenty years ago and there is no mobile or smart phone or Internet or modern means of communication and services and communication and free communication and wonder that we ourselves lived these conditions and live Now as if we have moved from planet to planet and we do not feel.

The fact that we do not know that every scientific research leads to a result or a modern invention took years, but because we see the picture from outside without attention to detail, we feel what we said above.

Cloning is a process in which access to a living organism is targeted using non-genetic cells taken from normal body tissues. Specifically, the non-genetic cells are meant to be the sperm cells of the male and the egg cells of the female.

This embryo is identical in terms of the genes in the nucleus of the primary cell with the person from which the cell was taken. If we take a cell from the hair of a man’s head and extract the genetic ribbon from the nucleus of the cell, the embryo will carry exactly the same gene. Reproduction process. How do scientists conduct this process? In the beginning, a physical cell is taken from the organism that wants to reproduce a fetus with the same genetic and genetic characteristics.

Proficient in: Stem Cell Research

“ Ok, let me say I’m extremely satisfy with the result while it was a last minute thing. I really enjoy the effort put in. ”

The scientists then empty the cell and separate its nuclei, which contain the gene containing DNA, and the genetic material extracted from the nucleus is 46 chromosome. The scientists then integrate the nucleus belonging to the first organism into an egg that is free of the nucleus of a female incubator, and then expose the egg to an electrical charge. The division of the nucleus of the primary cell begins. The zygote is the group of primary cells that begin the process of division until the embryo is formed. This embryo will naturally be pregnant for all the genes of the first organism whose entire genes have been extracted for implantation in this new embryo.

One of the most important applications of cloning is the production of new species and species from some plants, including rare plants. One of the most important applications of cloning is its use in the field of stem cell production, a large area that has become a branch of the same branches of science and conducts thousands of research in all universities of the world. Scientists see it as the solution to most chronic and debilitating diseases that afflict humans. Use this cloning in a way called tissue or therapeutic cloning by taking a stem cell from a tissue we want to reproduce. Then we integrate this cell with the eukaryotic cell cell and supply it to the electricity to begin the split and are implanted in a vital medium to produce an embryo. Stem cells are then extracted from the fetus, The tissue is intended for the process and then we can transplant it in a person that conforms histologically with this cloned tissue. Scientists are trying to clone stem cells to produce skin cells to replace burnt or highly inflamed skin or chronic diseases such as leprosy, vitiligo, other skin diseases and skin cancer. Stem cells that produce this process also have pancreatic cells, which are of great interest because if successful they will eliminate diabetes altogether. Scientists are also interested in researching the production of stem cells for testes and ovaries to treat infertility. So we imagine the possibilities in the near future and it was the cloning that some people feared. Therefore, the moral utilitarian theory is more clear in this case, it is beneficial to society and may be a cause of treatment for chronic and difficult treatment.

The human cloning process is still restricted by laws and ban in many countries of the world for fear of the impact if it happens on the human existence and human civilization if it is exposed in the future because of the cloning of the mutator of the mutants or a tyrant bloody and took the law makers a panic of the imagination of some scientists specializing in this Science. One of the reasons for human cloning is the need for large funding and the failure of experiments in more than 90% of the experiments. The results and examination of the animals in which the cloning was performed showed that the cloned animals suffer more than other severe immune and malignant diseases and diseases of the nervous system. Sudden death and all this delays the start of human cloning. But scientists are seeking to use it to transplant human tissues for use as transplantable alternative organs and this will achieve a great medical achievement, which will contribute to the treatment of patients with liver failure and kidney failure, diabetes and heart disease and blood vessels and research is to use stem cells by cloning in the production of nerve cells and this will be a great breakthrough.

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